Can't really help with #1. I would suspect the switch in the frame of the door.

#2 - the beserk electronics sounds like a flaky ignition switch. Encountered the same thing on a 560SL that I was test-driving before I bought mine. For the AUTO setting, there's a cabin temperature sensor. Don't know where it is on the SEL, but for the SL, you get to it by removing the glovebox. There's a foam tube that eventually disintegrates and needs to be replaced. I would suspect it's the same for the SEL.

#3 - I would probably start with the cold start valve or coolant temp sensor, but it really could be any number of things. I've been chasing idle problems on my M103, but not the M117.

#4 - Possibly tread seperation on the tires. If one is bald, then get new tires. Replace them in either pairs, or all four at once.

#5 - If they haven't been replaced yet, you're living on borrowed time. Replace the chain, tensioner and guide rails. $700-$800 every 100k miles shouldn't hurt too bad. Or, since it's labor intensive, you could change them yourself and save a bundle. Probably not more than $150 in parts.

__________________
Mike Heath
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino