jgl1, the earlier year MB's (not limited to W140) had wire insulation that was very poor quality. Rumor has it that the insulation was designed to be bio-degradeable. In any case, the insulation does not handle the heat of the engine compartment well. I suspect that during the trans removal, various harnesses were moved or removed. Any flexing could cause the insulation to crack off. This leaves bare wires which can touch each other and casue all sorts of electrical problems. I have a 95 S600, and I examined all the wiring very closely. The previous owner had changed a couple of them, because they look very new. Others had not been changed, so I rewired these myself. I'm including a link to a thread I wrote on another forum, you may want to look at it. There are some pictures of the insulation problem. Please note that I mistakenly refer to the MAF sensors as Throttle Actuators initially. I corrected that error later in the thread. Instructions for rewiring the Electronic (Throttle) Actuators are in my web page. MAF sensor rewire instructions are being worked on now.
http://www.mbnz.org/forums/forums/thread-view.asp?tid=1202133&start=1&fid=13