Dot 5 will drfinately trash a formally Dot 3 system. I cleaned out a Harley brake system that had been contaminated and replaced all the seals, etc. Since those brakes are such a small system any trace of the stuff will booger up a new rebuild, which it had done. I had to take it all apart, replace the lines, seals, etc. The other guy left the old lines in and they had that nasty DOT 5 in all the nooks and crevises. On a larger car system you might get by with flushing the system, but the silicone based Dot 5 is not compatable. DOT 5 is better, but I prefer Dot 3 as it is more common and can be found anywhere. DOT 4 is just DOT 3 "improved" and will intermix-I think. Check with a brake shop though.....Russ __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new Resources site http://smallbusiness.yahoo.com/resources/