The proactive approach, as has been mentioned, is to clean off the threads on the can and the cap before reinstalling. If you take the slip joint pliers to the cap, you distort the cap and make it even more prone to leakage. I bet if we made some teflon cap liners and used them when we first opened the can that the whole problem would go away.
Norm Furutani put us onto some high-quality storage jars from McMaster. If you want to do better than screw-top cans (or even worse, the standard hammer-lid paint can), I'd check out Norm's method.
If I had a lid that was really stuck, I might hit the lid with the heat gun and then keep twisting. I'd likely use a quick cardboard cutout (that's what empty cereal boxes are for) to keep the heat off the rest of the can. The more delta-T you can get, the more likely you are to crack it loose.
I have tried storing the cans upside down so that air exchange (diurnal breathing) doesn't degrade the paint. If you do that, you might find over a year or so that the can you thought you sealed has been weeping paint into your storage box. Naaah, that never happened to me! Right....
I suppose I could put some thinner on those blobs to see how readily they absorb it and become viscous material, as opposed to solid material. That would tell you whether dosing the can with thinner will likely have the desired effect. But remember, it is about the solvent migration. If the solvent can only reach the edge of the glued seam, it will have to migrate all the way thru the threads before it will break loose.
I have been using the stuff now for at least 10 years or so? I put the dates on the cans just to help keep track. If it hasn't dried out in the can due to poor storage, the stuff seems to keep working.
Something that might help extend the life of the paint is to squirt in some N2 as you close up the can. Reduce the oxidation. Not sure how vulnerable epoxy components are to that....
I think the real trick is to actually finish a bunch of airplanes that you have laying around, ok that I have laying around, thereby putting that good paint to use before it gets decades old and thicker 'n chewing gum on a cold winter day...? I just need to buy some round tuits. The extra large ones. A full case of 'em.
The Divot