Bro I just used some STP deisel treatment on my 1991 Pajero and had absolutely no problems what so ever,
I did not change the fuel filter or oil filter etc, just poured it in the tank at the service station and got her filler right up,
it's been around 2 weeks so far and I have experienced no problems what so ever, there has been a noticable improvement in fuel consumption, acceleration is marginally better, starting is much better,
if you can find the original STP (there are many, many, many fakes out there) just go for it without a second thought.
You just need to use it when you're getting your tank filled up to max capacity and then just drive around as normal.
Good Luck!!!!!