Fuel leak in 1990 2.5 Turbo

[Richard Eldridge]

I have been using biodiesel for about a year in my 90 2.5 turbo. I have replaced the return lines and several of the 5/16" lines with viton, but there seems to be another leak that I cannot see from above. Fuel seems to be dripping from off the oil pan.

Question: what could this be? How many and what size of tubing and o-rings do I need to replace everything that is likely to leak?

Many thanks for your kind assistance!