I own a diesel truck and car so this be more important to me than others, but, the TDI forum I read at has a deal going on for discounted Optilube. I have always used XPD in all my tractors since they are run a lot and sit for a while.

Diesel Fuel Lube ? The Best Additives Made for HPFP

From what I understand there is not much mark up on the product.... If you looking, I hope this helps.