The one thing I have learned about aftermarket valve cover gaskets for Toyota's is they tend to fall out of the groove during installation. It's not so bad when you catch it before you bolt it down but if you don't the mess is terrible.
The longer the valve cover the more trouble these aftermarket gaskets are.
I have never had a Toyota valve cover gasket fall out of the groove during installation the fit is perfect and the longevity of OEM can't be beat.
I just replaced mine along with the brittle spark plug tube seals (that cracked when I removed the valve cover) and the pcv and grommet which broke into a half dozen pieces. if you call Dan he will set you up with all the parts you will need (besides the valve cover gasket). I also changed the squeaky belts and the leaky o-rings for the distributor and speedo gear.