HF o-rings may not be the exact fit. If you do not have a new fuel filter/ o-rings, I would suggest just taking out the o-rings and inspect under a magnifier glass for damage. If they are smooth with no nicks, put them in boiling water for 5 minutes to un-crush and re-use. Also clean the o-ring seats and lube with diesel first. Maybe whoever installed that fuel filter did not do a good enough job keeping things clean and that's why it's leaking?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked