I cannot think of any reason why form-a-gasket would last any less time than other gasket compound. Infact I would expect it outlast other approaches. Preformed gaskets are just more convient and do not oose if you put too much on. Note that most toyota sumps are now put on with form-a-gasket.
Speak to James at Castle Hill Toyota......ive bought all these b4, only cost $11 i thing......with a bit of luck they may have them in stock......number is 96802233