I have a 1997 Mercedes C280 with 232.000 miles. The previous oil cap was aftermarket and it was very hard to twist off. Had to use pliers on a few occasions to help twist cap off. The pliers cracked the cap shell and it crumbled in my hands.
This time I purchased a Mercedes OEM oil cap and it is easy to twist on and off. The OEM cap cost a little bit more but the quality is better. The handle is designed differently for more leverage and grip. No oil leaks so far. Seems to be superior over the previous aftermarket cap. Always go with OEM when purchasing aftermarket parts. Yes it does make a difference.