I have a similar problem... only it's the opposite.
My oil level light won't come unless there's almost NO oil in there. I know it works because when I change my oil, and if I turn the key to position 2, the oil light does come on. But one time I checked my oil, it barely even touched the dipstick! And no oil light.
I think maybe the sensors just get dirty? Or mis-aligned?
2006 E350 w/ 155k miles (Daily Driver)
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!)