OK here is some more specific info for the archive.
I bought the Craftsman spark plug pliers (#947315) and a spark indicator # 19380, a pen that has a fuse that lights up and pulses with the current after placing the pen body over the plug wire. Neat.
Pliers and hand combined worked to remove the plug boots. I was told by a former 1989 420SEL owner that the boots need to be turned first then pulled out. Contrary to a forum poster that claimed rotating the boot does nothing...
I can not so far ascertain this point.
How to remove the distributor cap.
Remove the black plastic cover held by side tabs. Pull up and the thing comes off. It has tracks in the back side also that have to be fitted when replacing.
(allen wrench = allen key)
The dist. cap has three hex nuts. The two top ones are readily accessible and come off with a 5 mm allen wrench. (hex wrench).
The third one is located below and over the serpentine belt pullet etc.
Use a long armed allen wrench. Insert the longest arm's end into the hex bolt from the fan vantage point.
The radiator fan has one blade which is spaced farther apart than the rest. This area allows space to work within.
Use a 6 inch crescent wrench to grip the allen wrench arm from above.
Use the crescent wrench to turn the allen wrench and remove the lower hex bolt. Reverse for installation.
You must snap off loose the plastic plug wire cover plate (that sits on the valve cover) in order to allow the wires slack. This way you can pull off the dist. cap without having to disconnect any wires. Unclip the coil wire from the wire holder on engine body also.
Check cap contacts. Use sandpaper and an arced motion to lightly sand carbon from contacts. Contacs are concave so don't sand flat side to side.
Don't sand the carbon brush at the cap's center.
Do lightly sand the rotor's contact. It also has a curved surface.
Reassemble. Hand tighten the hex bolts. 'Torque' down the top two first then the bottom one last.
Cleaning the cap helped my problem a bit. It was not very dirty.
Now I need to remove all plugs. The pen helped me suspect the two plugs nearest the firewall.
I'll try atomizing water over the boots first.
my car has NGK plugs installed right now. 36K miles on 'em.