Thanks to everyone who replied. I really appreciate it.
The interchangeable thumb does sound like a good idea, but my thumb changes so much over the course of a night, as well as over the course of the season, that I probably would have to have 3 or 4 replaceable thumb inserts … just guessing.
I have looked at the foam tape, and maybe I will give that a try.
I have never liked the feel of white tape. It makes me feel like I am going to hang, and always wind up getting tape residue when fiddling with it.
I have tried an oval drilling before, and didn't like the snug fit of the narrower hole. I felt like the skin on the underside of my thumb would pull on exiting and prevent a clean release. It could certainly be that after so many years of bowling with a round thumb hole, I just need to get used to it. I think that my thumb actually seems to rotate as it exits the thumb hole, and the oval seems to stop me from getting out clean that way.
I would love to be fit by someone who really knows how to fit. I live in Central Virginia and would travel within the state (or perhaps even further) to find someone who really knows his/her stuff. I have been to many coaches over my "career", and most have told me my fit is fine. Of course that isn't the same as hearing it from someone who fits people for a living.
Contrary to what the "standard" fitting guides have suggested, I have a forward pitch in my thumb (1/4") … yet my overall span is close to 4-3/4 and 4-7/8. I recently switched to Bill Hall's "tri-grip", and talked to him over the phone to settle on a span … but that isn't the same as being fit in person. Somedays the fit feels good, but some days it just feels bad. I wish I could describe it better.