I noticed I have oil leak coming out of my oil filler cap and made a mass on top of the engine in my W124, especially after a long drive. It seems the problem may be more severe than I thought because I can see oil residue on the hood pad as well. Do I need a new oil filler cap? Do any of you change any of the caps in your engine compartment? I read it once that it is advisable to change all your caps - oil filler cap, radiator cap and gas cap every so often. Any suggestions?

87 W124
95 R129
98 W163