Replace the joker annually and also lube annually (maybe semi-annually if you live aboard) with SuperLube or other thick Teflon grease (the kind that comes in a tube, not a liquid or spray). To do that, remove the pump from the base, stick the tube nozzle into the pump and give it a healthy squirt. Pump a couple of times to spread the grease all over the cylinder walls...put the pump back onto the base...you're done. Best time to do both is to make it part of your spring recommissioning.
This maintenance schedule should keep a PH II working reliably for at least 20 years, if not longer.