starter Motor Problems

[Tony Smith]

I think Alex is right, there is movement inside the starter and something's shorting out. You seem to have the complete set of compatible bits, the starter should just mount up to the bellhousing neat, no spacer.
With the long bolts tightened up with nut, is there any radial or thrust play on the shaft? Besides the bearings in each end of the starter, the Canadian starters also have a thrust washer to take up any play. I'm not intimately familiar with the internals of a Lucas starter, but perhaps this ought be looked at and/or replaced when doing the bearings.