i'm no expert, but i have replaced front and rear bearings a couple times on my 750's. the first one i was scared to drill too deep and had a hell of a time getting the retainer out, and even tougher time getting it back in. after that first one i went ahead and drilled deeper and the retainers went in and out pretty easily. i'd try drilling a little further. use a file to clean up the threads on the retainers before you put them back in. again, i'm no expert, just telling you what worked for me.