Ok, here goes, I am one of those beleivers. I used Slick 50 oil treatment twice on my 90 vanagon that now has 181,000 miles on it's original engine and still runs great. Yes the head gaskets went at an early age of 64,000 miles and they have not failed since. I know that had nothing to do with the Slick 50. I am not sure my engine has lasted so long because of the Slick 50, but I don't think it has done any harm. I added the Slick 50 at 13,000 miles just before a trip to Florida. She was nice and new then. I then added Slick 50 at 90,000 miles. This past August I drove down to Myrtle Beach SC. I stopped on the way back at The Bus Depot in Penn. to replace a window crank that broke on the trip. Those guys at The Bus Depot are great. Well when I got back I replaced the upper and lower ball joints and got a wheel alignment and new tires all around. Almost feels like new again. By the way the tires I purchased for those who are interested are Pep Boys Futura GLS Super Sports, 215/70-14. They are very stable and seem to have good traction, I will know better this winter. Take care.  John