would suggest a good brand of diesel fuel additive such as "lucas" or "Cen-Pe-Co" etc....
I don't have many years experience yet but I have been working with Diesels for some time (my brother kind of started it with getting in to WVO)**,also my dad is in to selling "Cen-Pe-Co" products and they give a bunch of info on the new fuel and yes is does harm to the older engines with more mechanical parts(mostly injector pumps)
I've got an Isuzu NPR that we use for my dads business and it's only got a 3.9L 4cyl and it's easy to tell a very little bit in HP loss or gain, and he said on his last trip that he forgot to put fuel additive in for the 12gal that he topped it off with(in a 30gal tank)
he could tell that it was lacking HP!!
**My Brother and I built THE COOLEST GMC 2500 4x4 Suburban out there (that I've seen) it's got a 5.9L Cummins Turbo Diesel from an 89 Dodge, and a 5Ton Eaton Road ranger RTO11609A Transmission, and a divorced NP205 ford transfer case, it was a LONGGGG job but it is AWESOME to drive and will pull a 10,000lb.+ trailer with ease(of course the engine was turned UP we estimate it to be around 300HP) the drive shaft snapped once and then a stronger one was put in and then the spider gears blew!! so it was learned that you've gotta be careful with that nice ceramic clutch AND THE throttle!!! and we're thinking of putting a DANA 80 under it when time permits!
Any ??'s send me an email (email@example.com) I'm looking to do more conversions so let me know if your interested!!
"The use of plant oil as fuel may seem insignificant today. But such products can in time become just as important as kerosene and these coal-tar-products of today." Rudolf Diesel