[embee]

Never use any aftermarket OIL additives. Use a decent oil in the first place and it will have all the additives you need. Some of the snake-oil additives are positively nasty (those consisting of principally chlorinated paraffins, very impressive anti-scuff demonstrations but turn into hydrochloric acid when heated in an engine, 1930's technology abandoned by the industry. Very cheap to make so attractive to flog).

Fuel additives can sometimes be a help in certain circumstances. IPA will help to keep water contamination from messing everything up (but won't solve everything!), but you shouldn't be getting the water there in the first place, so sort out the real problem first.