kaching

I have a question for those that have successfully rebuilt turbos. After removing the turbine seals, I found a layer of really tough carbon build-up? At least, I think that's what it is.

Should I have started to remove this or just left it alone. I glass beaded the parts, but with the old seals in place. Should I re-clean them now that I can get to this spot. The reason that I'm asking is this stuff is seriously tough to get off.

Thanks.