I bought a new cap from the dealer today....(same price as Phil w/ shipping).

The parts guy replaced the black (rubber ?) seal that came on the cap with a blue one (think he said it was neoprene)...said it was an "updated" seal.

I'll see if this is a fix and post results. Have to wash the car first.

By the way...just to note.....I've been trying various mixes of biodiesel, from B20 to B99....sometimes 50/50. Don't think this has anything to do with the leak at the filler neck though...as all the previous cap seals seem in good shape.....and the one on the w124 cap is cork???

But every time I look there's fuel standing in the crevice of the filler area underneath the filler neck and I do notice that the black drain tube in the fill area looks a bit funky....??

Does that tube drain back into the tank ...as I expect?

Car runs fine on all biodiesel mixes....and no clogged filter so far .....but keeping an eye on misc hoses/ F.I. pump area for leaks.

Warren