Hello; I have seen that problem 3 times, where the rear bearing blew apart leaving a tiny ring to get out of a deep hole. Usually (2 times) heating it in an oven at 250* and smacking it against a block of wood, get's it, but you've tried that with no success, so you might have to do what I did on that Saito 80 I had that did the same thing. What I did was attach the 90 degree head to my Dremel tool and put a cutting wheel on it and cut through the bearing outer shell at 3 places, which then came out. I don't have to tell you to go carefully and don't gouge holes in the case, just the bearing. I found for the second and third cut, that it wasn't necessary to go all the way through the shell to weaken it enough to split it when hit from the front. Even if you touch the case with the dremel, after you clean it all up, there's no where for the oil to leak to, and a little scratch on the bearing mount surface won't matter to the running of the engine.. I admit that this works better on larger bearings, but a steady hand, and ten minutes will have the broken shell out.