A tank to bowl gasket from the hardware store will probably not work. More power to the tinkerers...but for some of us that is out of the question...REPLACE the energizer module with a retrofit from sloan. They make retrofit Flushmates to fit the major brands which used the PF-2. Just google it.
I have a Sloan Flushmate in my house from 1992. Never any problems. Replaced the supply group once and the cartridge about 3 times in that period.