I have a 1987 300E. The car has a problem when accelerating from stop or low speed (while on 1st gear) it feels like it is trying to go to 2nd gear and 2 second after that you feel like someone pushed the car and it jumps forward a little changing to the second gear. I know the car has engine oil leak problem and I have to refill every 500 miles. What does the problem here? And what is the best Engine Oil for my model?

Your car starts on second gear. As far as jumping between gears, do a search, there are a couple way to adjust it. Steve Brotherton touched this topic before. It worked for me.
Good luck!

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J.H.
'86 300E

Yeah, you should adjust your BOWDEN cable. I believe you should loosen it a little bit. Do a SEARCH to find out more info.

Oil depends on your climate, if it gets real cold, use 0w30, or 10w 40 or 10w 50. But if you have climate like So CAL (never really gets below 40), then 10w 40 (or 50), or 20w 50 are good oils. If you are in the warmer climate, a thicker oil would be better... it might help reduce your oil leak.

GOOD LUCK!!

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)