I am wanting to change oil for the first time since I bought this car. It has a plastic cap for the oil filter similar to the cap that was on 1999 E300 that I had, however there is not a hex feature on top to put a socket on to remove the cap....what tool do I use to remove the oil filter cap? Thank you in advance.

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Current:
1985 300D aka Miss Margaret
1991 300SE aka Alarice
1995 SL320 aka Samantha
1997 K1500 Silverado
Past:
1999 E300 ex-wife got it and let her son ruin it
1984 190 2.3 ex-wife got it and let her son destroy a great car
1985 300D (CA version) aka Maybelline lost to deer at high speed.
1981 300D aka Madeline (went to salvage at near 400k) rusty, yet best car I ever drove
Wishlist:
McFarlan TV6 (only a few privately owned)
ReVere with Rochester engine
1917 Premier (only one left)