Is it possible that using the incorrect motor oil viscosity can cause wrong-timing-like symptoms on a motor? For example, after I changed the oil on my 92 400E with 10W-30, the engine started mis-firing and idles rough? All I did was replace the oil and oil filter. Is the 124 really that sensitive?

 

doubtful, probably just coincidence.

 

Chassis221 - I bought the car used and it didn't come with the owner's manual. I've looked around but can't find motor oil specs for it. Do you happen to have any information regarding this? Should I have used synthetic rather than conventional dino juice?

 

Never mind - I found it at the Mobil website:
Mobil 1 0W-40 Full Synthetic

 

actually your car doesnt require synthetic. if you use it it might actually leak oil more but this is debateable. the oil is more slick and thin and it can leak from every possible spot. id stick with regular oil if i were you. when i used to use synthetic in my nissan it made alot of noise as compared to using the regular oil.