I had some old Winn's fuel conditioner that came with my car's extended warranty in 1984. I ran across several bottles of it in the garage last year. Rather than take it to the haz waste recycling center, I added it in 2-3 oz increments to my 2002 Linc. on each fill up. Can't say I noticed any different one way or the other. I treated it as old stale fuel.
2002 Lincoln Cont 4.6L DOHC/ 81K mi /PPlat 5w30/FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs