Ditto to R19... my Dads boat is running a 1992 Evinrude 150 intruder. It has been mounted on two different boats and gets heavily used. It has also been very well maintained. Always used XD25 and never added fuel additives except stabil to winterize. It still purrs like a kitten although it is more cold natured than it used to be.

One thing i learned in the car world which may be different with marine fuel additives, is that gas already contains everything you will find in a bottle on the shelf at autozone, they are just concentrated when you buy it as a fuel additive. This i learned from my father-in-law who is in the petro-chemical business...