I rev mine all the time in Park...lol. Am challenging the trans to blow so I can install a Getrag 5 speed. Not really. If the A-clutch input shaft seal is worn, then you can overpressurize the A-clutch in Neutral or Park only if the car was been put in drive just before. After a long cool down or after initial start up, you can rev the engine in P or N without incident. The fix is to replace the steel O-ring with a Teflon seal. Winfred has a superb write up on the procedure as he has done a lot of them.
George