Well a bad battery ground is never good, one of my BMWs would not even start with semi loose battery connections. I am not sure how sensitive these cars are to charging systems, but verify the alt connections and its output.
I know one of the body grounds is from the steering pump bracket to the fender area.
Well consider this also: the newest M116/7 here in the US was built in 1991. That was 19 years ago, maybe 20 depending on build date. The early ones should have come out late 1985 which is 25 years ago!
So most of the rubber under there is in dire need of replacement.
Pull the air cleaner assy off and nose around. Just touch and squeeze all the stuff to see if it is pliable, if not... well that would be a good place to start before attempting to further fix issues. Do not forget, the intake manifold is a two piece... so the eight o-ring looking seals need to be replaced also. This is a real PITA. Also the fuel distributor boot to throttle body shrinks with age.
Four and three way connectors go bad too. Any oil leaks are vac leaks...