Robert, like you I found this site a great help and spent DAYS going thruogh it after spending over eight months & £2k trying to get my 93 sl300 going. Its a long story but mine would stumble all over the place and would'nt really follow a patton except when the engine was really hot or it was hot and raining.
My mech worked through every thing & and changed loads, it would run perfectly then get worse. I was driven to distraction and nearly bankrupted by the bills. I finally found out MYSELF and I really don't have a clue it was the plastic plate Behind the rotor arm. It had a small nick on the top of it and let all the damp air in and sent the cap green on the contacts.
£45.00 was all it cost to do!!!