My '99 MB started being very hard to start in mid-winter. Blaming it on gas, cold, etc., I just cranked it until it started. (I grew up with carburetors and knew that choking was not the solution.) It continued on and off during spring - I took it one step at a time: change plugs - no help. Change fuel filter - no help.

Finally, last week I took it to the M/B dealer for a fix. Wow! The rear main was leaking oil into the bell housing and the oil - about one quart in the housing - was interfering with the operation of the crank sensor.

Oil cleaned out, crank sensor cleaned, rear main seal replaced. It now starts easily.

Anyone else with this problem and its rather expensive (not a shade tree mechanic's job) solution - pull transmission, etc.?

 

Crankshaft position sensors are a common problem. So are leaking rear main seals. They could have been related. To replace the crankshaft position sensor is easy and anyone can do it. Replacing the rear main seal involves removing the transmission. Its about an 8 hr job to replace the rear main seal.