I think I have finally  figured out why this engine I bought failed.
Up until 1993 Mazda used a one turn round wire coil spring to press
the corner seals against the end housing. Apparently the spring
found it way out into the space between the rotor and the end housing
and marked the rotor as you see in the picture below. This of course
defeated the corner seal and carbon build up in that area causing the
apex and the side seals to stick in their slots. 

I mentioned this to Dennis Hayes and he said; Oh yea I have seen that happen. 
Mazda fixed it in 1993. Use the 1993 and later flat steel leaf type corner 
seal springs when you over haul your engine. 

Paul Lamar
 
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