Pump being replaced had low usage but was measured in situ to be shorted internally -> Found washer stacks had been pressed between the ion pump body and the magnets for some reason?  Don't know who had done this or why but, in theory, it shouldn't cause a problem with the operation of the pump -> Measured short went away when pump was removed from frame however -> was the pump body distorted enough by external washers to result in an internal short between the tight clearance electrodes? -> Will retest removed pump and reuse if OK.