From my experience with my head gasket, and talking to my local mechanics, and the posts on this site, I believe you can let your gasket just leak only until it gets so bad that you can't stand it anymore.
I took my car to Mr. MB Motors that Ashman recommended in the Good Shops forum. Enrique has been a MB dealer technician for about 30 years, and said that my leak was among the worst he has ever seen.
My leak was so bad that oil was pooling on the floor of my garage. The leak was so bad that the oil residue on the engine block was smoking when I would drive the car. When I parked the car in the garage at night, the garage would smell of burning oil.
When I took the car in, finally, to Enrique, he put it up on the lift, and the whole undercarriage of the car was covered in oil. The tail pipe, catalytic converter, exhaust manifold, etc. were caked in wet oil. It was a helluva mess.
It seems that some gaskets leak very slowly and will stay that way for a while. My went from a tiny drip to a waterfall within 1,000 miles.
Regarding the wiring harness, from '93-'95 on M104 engines - they are all bad. It's not a question of if, but when.
If you do a search, you'll seen numerous posts of owners whose wiring harness went out and ruined some very expensive parts with it, turning an $800 wiring harness replacement cost into a several thousand dollar repairs, taking out throttle actuators ($1,100 part), EHA's, idle control valves, computers, etc.
I don't understand why anyone would let this go, considering their high failure rate and the possibility that it will take out much more expensive parts with it.
Check out these posts:
http://www.peachparts.com/shopforum/showthread.php?threadid=38054&highlight=engine+wiring+harness
http://www.peachparts.com/shopforum/showthread.php?threadid=40246&highlight=engine+wiring+harness
http://www.peachparts.com/shopforum/showthread.php?threadid=40795&highlight=engine+wiring+harness
http://www.peachparts.com/shopforum/showthread.php?threadid=40246&highlight=engine+wiring+harness
http://www.peachparts.com/shopforum/showthread.php?threadid=18441&highlight=engine+wiring+harness
http://www.peachparts.com/shopforum/showthread.php?threadid=6064&highlight=engine+wiring+harness