here is an example of where the damage getting place.
green arrow:shows the grooves towards the apex seal(i 've also draw some for example).

blue arrow:shows the position and size(in scale) of the missing piece.

brown arrow:that's what i meant compression groove.

i think that you are going to be surprised with my skills on drawing.(my real name is picasso,pablo picasso)

 

Very good! Yeah, the brown arrow points to what we call the bathtub. Put that rotor on a book shelf, or use it as a paper weight. I forgot to post my pic earlier, as you pointed out I'll get it, but its nowhere near as nice as yours, Picasso

 

Red= where I was guessing the grooves and hole where.

Blue the bath tub.