On my last visit to the tire shop for my '82 300SD I got some Dorals (I thought they were cigarettes, but they're also an Indonesian tire) and an alignment. Turned out one of my braking support rod bushings was going, and also that my rear springs were shot. Consequently I have just replaced them. I spent half the day trying to use a spring compressor and the other half of the day doing the job right. Short form, drop the rear of the subframe and they will fall out.
On my first search all I really found was a lot of advice on which spring compressor to use, but on my second search (after a frustrating morning) I found PeachPartsWiki : W126RearShocksSprings which suggests dropping the front of the subframe, by disconnecting the bolts for the subframe bushings. This is just wrong. Unless you want to inspect those bushings, leave them alone, you will only disturb them. If you instead put a jack underneath the differential, pull the four bolts for the differential mount (which is the rear subframe mount, too) and lower it down, then when it reaches full extension you can push down on the suspension arms and the springs will just fall out — at which point they will actually be pointed at a notch in the frame that looks like it was designed just for this purpose, when you get to that point anyway.
The removal procedure is actually slightly more involved, so you can use the PeachParts page to get through most of the process. There are likely additional complications for drivers of vehicles with ASR (automatically self-leveling rear suspension.) First you remove the rear seat - the bottom comes off with some little levers near the corners, and the back comes off with three 8mm-headed screws. Then you can remove the round plastic plates which cover the tops of the struts. There's more covers there for access to the ASR fittings as well. The struts are double-nutted with 17mm nuts, so you will need two 17mm wrenches or one wrench and a socket wrench with a 17mm semi-deep socket as well as a pair of long-nose pliers. You will also want to clean the threaded part of the strut rod with a wire brush before removal.
Next you're going to need to jack the vehicle, mount it on stands, pull the wheels (with the e-brake on you should be able to take them off, but break the lug bolts loose on the ground anyway, 17mm socket) and also remove the sway bar from the end links (17mm) and dismount the brake calipers and hang from the sway bar (19mm) as well. You'll also want to remove the struts from the vehicle, there's two bolts with 17mm heads at their bottom. At some point by now you will want to have dropped the exhaust by prying off four rubber isolators, which will probably be cracked and which should be replaced. Put a floor jack underneath the differential, remove the four bolts (15mm) and lower the jack, and the entire rear subframe will pivot on the bushings. Lower it all the way (the vehicle only needs to have been jacked up to where the wheels are a couple inches off the ground for clearance) and push down on the wheel hub area and the spring should fall out.
On the way back in you will note that the spring has to be clocked a certain way to match the lower seat properly, and that there is a rubber bushing at the top. This bushing will have a slight indentation from the top of the old spring, but you can ignore it. The bottom is critical however, at it matches the end of the spring that's not flat. The flat end goes up. Put everything back together in reverse order. When you get the subframe lifted back up you'll probably have to do a little work to align the transmission mount so you can get the bolts back in. I used a tool whose name I don't rightly know; it's a screwdriver with the shaft just turned into a spike, tapered near the end. You can insert this through the rear bolt hole on a side and right through the thread, and then use lever action to line up the front hole and get a bolt in. Repeat on the other side, but this time pay attention to the dirt marks on the bottom of the vehicle and put it right where it belongs, then tighten it just enough to keep it from slipping. Go back to the first side, pull the bolt out, and then get the first side lined up where it belongs. Now you can put a rear bolt in with thread locker, tighten, remove the front bolt and apply threadlock, then put it back in, etc. I used thread locker on every non-lug bolt I disturbed because this is all pretty critical stuff.
I also replaced my headlight doors with replacements from FCP Groton (they have the left side, too, of course.) They shipped them to me in two days, and putting them on is a matter of pulling out the corner markers, pulling off a trim piece (#2 philips, 8mm socket on 1/4 drive ratchet) and popping the old ones off with a fairly ordinarily-sized slotted screwdriver by bending the clips built into the headlight housings. If you're doing a long-wheelbase headlight lens replacement, the easiest way by far is OUT OF THE CAR, because you can bend the clips by hand. If you've already installed them, though, it's not too bad. You can access the third clip from below. You could probably do it without removing the headlight trim but then you couldn't see what you were doing with the third clip. FCP Groton is one of my favorite discoveries. I'm still likely to give Mercedes Source my money more often because they provide a fair amount of tech help and many parts ship with how-to instructions, even when they both have the same part — their prices are pretty close.
Finally, a word on Jacking the vehicle. You could spend $120+ to get a pair of flat-topped jack stands. You could spend $20 to get a pair of almost flat-topped jack stands, and another $20 or more to have someone chuck them up in a lathe and turn them flat, then have to find your own rubber pucks. You could even use hockey pucks drilled out and bolted to the top of a jack stand, but they'll eventually break which means they'll possibly eventually damage your car. Or you could just get a couple of bolts that just barely fit into the holes where you mount the factory tire-changing jack, which stick out a couple inches (about six inches long overall) and lower THOSE onto jack stands. You'll need pretty tall jack stands — too tall to really go anywhere underneath the car, but too short (for example) to hold up a lifted 4x4. I have one of them (don't ask) and I made a stack of 2x4s topped with some angle bracket to hold up one of my shorter stands on the other side. Because you have a hard metal to metal connection it's actually a more secure stand than using rubber-topped jack stands, and it's cheaper, too. The threads of the bolt will hold it VERY securely in the hole; I've deliberately done quite a bit of sideways pushing before I got under the car, and it's really fairly amazing. Some people have also built (welded) jack stands which install into these holes — if you build them well this provides absolute protection from sideways movement. There are even trailers designed specifically for Mercedes which use the jack holes as retention points.