For those who manage to score some MMM sealant to de-leak your old cats: this urethane based glue contains isocyanates and gets ruined quite fast by air and water getting through the screw-on plastic cap.

Here is how to save it: cut a little disk of aluminized plastic seal from a fruit juice jar, gum packet, tire patch, etc. Be sure the patch JUST covers the sealant and the top of the tube opening, and carefully screw the top back on.

It will now last a LONG time- almost a year so far for last spring's tube. Previously I lost several $$$ tubes of this great stuff between uses, even after drilling out the hard stuff.