Hi, I went through a similar ordeal and feel your pain. There isn't a whole lot to do other than use a lot of elbow grease. You may even have to get creative. Below is a paragraph I posted a while back when I had to change out the wires on my car, a 1991 300E W124:

"Changing the plugs and wires was an ordeal and took me 4 hours - I wouldn't doubt if they were original too, or at least very old. Each wire disintegrated as I pulled on it, no joke. I had to bend each boot and crack the spark plug insulator within so that I could break and rip off the top half of the boot. Once the top was ripped off, exposing the shattered spark plug, I had to use 3 bugle-head screws driven in between the remaining boot and spark plug very slowly with a stubby screwdriver. Then I grabbed 2 of the 3 screws with a pair of pliers in each hand and wrestled with every ounce of my energy in order to get the remaining piece of boot off. My knuckles were bleeding pretty quickly. Once the boots were removed, I used my finger to suction a straw to the crevice tool on my vacuum cleaner. With my mini suction tool, I carefully vacuumed each spark plug recess and got all brittle plastic and broken ceramic insulator out of there. Then removing the plugs was incredibly hard - I used a 1/2 inch breaker bar with a 3/8 inch reducer to break each one loose. Fortunately, the threads in the cylinder head were not damaged, and lubricating the new plugs with WD-40 greatly assisted installation of the new plugs. The old plugs, by the way, looked fantastic - the gap was HUGE, I mean 3 times what it's supposed to be, but the terminals were dry with no oil, no blackening, no soot, just a very nice off-white color with all electrodes and insulators intact, though very worn looking. Again, I wouldn't doubt if these plugs had been in the car for 118,000 miles and 13 years. The cap and rotor were atrocious too - I don't know how the car ran so well. Interestingly, changing all these things did not result in any noticeable idle improvement."

Hope this helps you more than it scares you!

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280