The IP on my '00 VW Golf TDI leaks with ULSD. The problem disappears with B100.

tdiclub.com has done huge write ups on the subject.

Some think its ULSD. Others that BD makes the seals swell - no BD and the seals shrink to below original size and the IP starts to leak.

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JWJ
1983 MB 300D - > 430,000 miles - Deep Blue - Bilstein Comforts - 0-60 in 24 seconds - 27MPG
1985 MB 300TD (wagon) - > 275,000 miles - Manila Beige - Thule rack - 0-60 in 18 seconds - 22 - 25MPG
Biodiesel, Mobil Delvac 1, and Viton fuel lines!