Hi B_S
Yes the thought had also crossed my mind, I've pretty much thrown out all the half used cans after the building of my neighbours machine.
I also feel that the paint has skinned up and pieces of that are clogging the passageway.
As MF suggested maybe as you have some half used cans left see if you can exhaust the remaining propellant and then cut it open and have a Captain Cook.
Will be great to see what the results are.
Cheers,
BB.