I recently had trouble getting the plug wires off my '91 300E and almost had to buy the special pliers. Once I did get them off, I sprayed the inside of the boots with HD silicon and now they come off with no trouble. I've also used it to ease taking the air cleaner off the throttle body, lubricating the throttle linkage, easing the removal of plug wires from the distributor and on other rubber seals in the car.

I highly recommend getting a can of the stuff for both car maintenance as well as other uses like lubricating parts of the garage door and opener.