I know what you mean! Before you close the tube grease the threads and cap it. I have a 6 month old tube I've used for a dozen repairs still good. Before I started greasing the threads the tube would harden up in two weeks. Oh and remember to get all the old grease off the tube tip before you use it again. Dont take much water vapor to cure 3m5200
Thanks, that's a good idea! I just checked the cap of the 3M tube and I realize that it's indeed quite loose (a lot of play between the threads of the cap and the threads of the tube). I can see how greasing the threads will slow down the entry of oxygen and water vapor into the opened tube.
I'll try it on my next tube of Aquaseal as well.
I keep my Aquaseal in the freezer for longer shelf life.
Thanks! I'll try that, too.