Maybe it's just me, but 3 years ago I bought 4 nine ball m9 gaskets. They came shrunken and dried out with a thick film on them from drying out. So I've avoided their rubber parts since. I probably got a older stock.
I will say however, certain pistols like the hi capa have a tendency to damage the back middle section of the gasket over time from the bb feeding bar on the nozzles rubbing them before it reaching the section that seals. Tends to take a bit out of it after awhile. Even stock tm nozzles do it. It's easily fixed with slight modification to the nozzle, but still annoying, most wouldnt notice such a petty thing tho.
Honestly, I've seen more than gasket condition/height effect the seal to the nozzle. I've seen nozzles with different dimensions screw over the seal, seen aftermarket blowback housings with different dimensions mess with the seal, worn out mag catches, and lastly grips that have too much slack allowing the magazine to fit poorly... Not to mention a old gbb having its rails and slide wear out increasing the gap. There is the option of gasket spacing if one is desperate. Another thing that probably doesnt help squishing seals is leaving the magazine in for months of storage.
Its sad how many kids run their gbb guns with no knowledge on how to maintain or improve them and just spit gas out.