Rick Kim over at RKT56 recently rebuilt my FRC's differential with all new C6Z springs, clutches, seals, and a set of 4.10s to top it off.
I originally inquired with him in the summer of '16, and although I didn't pull the trigger on the rebuild until this past January, he still honored the price that he had originally quoted me for. That was pretty nice.
He was even kind enough to not only answer all of my OCD technical questions (usually within a matter of a couple hours), but also to throw in a small spring that I needed to replace in my T56 (the part was no longer available through GM!).
I'm just finishing up the break in miles and am very happy with the unit so far. Can't wait to really get on it!
Overally very pleased with the entire experience - not only the technical quality of his work as well as the customer service. If I ever need any more work on my drivetrain, he has earned my future business.