Started taking out windows to reseal. Planned on dynatron 550 as per EastCoast Cb. The old hunk cane off bus sides easily. But, I am having a hard time getting it completely off the aluminum frames. The old stuff is a weird material that is still pluableafter 20 years. It is grey and I can scrape it off and ball it up like itís rubber or one of those grey art erasers. Called 3m and they said of course that surfaces must be completely clean. Is this clean enough? Any one know if the 550 will stick to this residue? Anyone know what it is? Should I get butyl instead? Please help on way to auto body supply store.