Nope, this was a brand new motor, I believe one of Bill's stock. Oddly enough I saw a similar looking thing on an earlier one but never connected the dots.Are you sure that that wasn't some former owner's hack?
It doesn't seem like a good idea to me. I wouldn't think that the tape's thickness would have a desirable effect on the gap between field and armature. But I'm not an engineer.
The big problem is it doesn't support the magnet completely. So over time the natural vibrations can loosen the magnets. Maybe this is what the big problem with the fat motors is....
Hey, maybe you should make an offer on my pile of ETs. You'd get some spare motors that way. And a spare ET, one with a Real Controller. (I'm yanking your chain a bit. :-)
Then I would have to get rid of my rotting E15 that I welded angle irons to the frame. I should get it running this fall, if nothing else I can drive it around the field....