What kind of oil filter do you have, the spin on type or the kind that goes in a permanently attached housing on the side of the block, with a removable cap?
If it is the latter, the cap should have a hex in it. My old C230Kompressor Sport had a black heavy duty plastic cap, and I bought the MB tool, which grabs the outside flats of the cap. On my 1998 E300D Turbodiesel, the cap is so big around you have to use the hex molded into the top to remove it. MB sells a tool for that too, but so does Sears for about $7. I think it was a 36mm hex. Anyway, you cannot remove these by hand unless you have a bionic claw. You need a wrench. If it was a spin on unit, I would agree most of them, depending on access, should be readily removeable by hand unless you put it on too tight.
Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)