My old Mistral was built in 1970 and the monel tanks were fine. My trawler's tanks were built in 1980 and also don't leak. I'm with Brian on this one. Why are you concerned with your 1985 tanks leaking?

My only advice is to put your fuel polishing system's pickup tubes close to the bottom (mine are about 1/2") and your engine's fuel pick up tubes much higher (mine are about 3"). After having all kinds of issues with crud in my tanks, I've now travelled 500 miles with no problems whatsoever.