March Pump/Replacement Head Magnets Rubbing (Sometimes Stopping) in Toolbox

I bought a replacement head for my original March Pump and build a pump toolbox with the old pump/new head and a second March pump. The second pump installed no problem but my original pump is having issues.

It seems as the though the replacement head is rubbing against the pump spinning magnet. If you fiddle with it you can get a clean connection but I can't seem to get it clean by screwing it in and leaving it.

Sometime it will rub so hard it stops the pump. I tried trouble shooting by using the new pump head on the old pump. No luck. Also, the magnet spins fine when the head isn't attached so I'm wondering what could be going wrong.

Slide the motor drive magnet back towards the motor 1/32" to clear the SS rear housing.
I would find it rather hard to believe the drive magnet ID and rear housing impeller bulb is
that far out of concentric to cause the impeller magnet bulb to contact the magnet.
Even the Chugger parts interchange with March without any concentric with rubbing problems.
If the motor adapter to pump are sandwitched by the toolbox which is not parallel or the same thickness
the head will be at a different angle than the motor causing binding.
Pressure cast plastic parts like toolboxes are tapered to release the part from the dies, this may be your problem
and just got lucky with the other pump. Check the simple possible flaws or problems first.