AC in a 240 huh…you have to block off time in Outlook for onramps.
I still have my gasser W116 (also with crank windows lol) but havent ordered parts in forever. I think I used to use Peachparts sometimes? And EBay of course.
The locks and AC are probably related. Even the manual AC has vacuum pods I think. Buy a Mityvac and start chasing vacuum leaks. Probably cracked runner connectors, but if your trans shifts 1-2 hard too there’s a bigger leak.
Timing chain can be done in the car. Get the manual on CD, shows you everything.
Keep mechanical oil gauge, electric ones are junk. Bet you anything the flare fitting on the back is just loose. Screw it down, or replace the gauge with another one.
You’ll probably get a keybhang or two resolved by wiggling before your key gets stuck. Keep a light key chain and I think a little graphite lube in the lock helps, but you can preemptively just replace it with a new cylinder from Mercedes, keyed to your code. Or you used to be able to. At any rate a hung key is bad juju.
Oh lucky you, those are awesome.