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Reviving this Mach 5 thread.  If not used for a couple of weeks the pump motor would not turn.  I would use the tool I made to break it loose and it would work.  I removed the pump and disassembled it to replace the seal.  The spring on the seal was clogged with mineral deposits and would not move.  I soaked it in vinegar which cleaned it up & is like new with good spring action.  I had wondered why when I used the tool to break it loose it would flex before releasing.  The ceramic seal is mounted in rubber which caused the flex.  I will save the seal for emergency use, a new one from Headhunter is on the way.

To disassemble the Mach 5, remove the 6 long screws with a 5mm allen wrench & pull the pump end off.  Remove the small plug covering the end of the armature and use a screwdriver to hold the armature while removing the 13mm nut from the pump shaft.  Slide the pump from the shaft one piece at a time being careful to not break any of the plastic pieces.  Slide the spring loaded seal from the shaft and using a pick, pull the rubber mounted ceramic disk out.  Installation is just the opposite, do not touch the seal surface with your hands and don't pit anything on it.  No oil, etc.

Thanks for the write up Jim and the pictures! I am sure this will help someone, if not me down the road some day.

I have had some intermittent issue with mine wanting to keep cycling. I had assumed it was an air pocket in the pump, mainly because it seemed to happen when I would connect city water to fill the coach and forgot to turn off the water pump and it seemed to cause this cycling. To get it to stop I usually turn the pump off and connect to city water and run the faucet at full open to clear any air out of the system, seems to work to stop the cycling issue. 
I will take a closer look and see if maybe its leaking at the seal and that is what is actually causing it to cycle.