I'll check for that seal, thanks Mike.

Well I know that the cap/seal is leaking! I may have not made myself too clear. For example, what is the purpose of the cap? If not to only contain the oil in the crankcase, but hold pressure too? So what would happen if you drove without an oil cap, pretending you didn't care about the loss of oil, but the oil pressure?

Sorry this is kind of confusing!

__________________
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!)