Bendix AD9 rebuild

I am going to do some maintenance on my Bendix AD9 air dryer, cartridge=pretty straight foward. The check valve only 2 choices after I determine thread size.

On the purge valve, hard seat kit and soft seat kit difference is the first is just the purge valve rebuild kit in existing housing and second purge valve is already in a new or reman housing with heater just install a couple of Orings and bolt it in???

Would you use aftermarket brand for this if so which?

thanks again,,,,,,,,

 

I replaced my Bendix AD9 wirh a SKF remaned air dryer. Almost 2 months latter it build no pressure and keeps blowing air out the purge valves exhaust port.
Of course no warranty on the unit, replace the purge valve???