Same thing happened to me, I called McMillan and they had me send it to them. They ended up replacing it under warranty. Other than the wait for the replacement it was a painless process and McMillan customer service was excellent.
In very abusive off roading like the bouncers in the south east, 60's went in the scrap pile and were replaced with 40 spline 14 bolts and Dana 80's with RCV shafts.
Me and the guys that I used to rock crawl with got 1.5 seasons out of a low pinion 60 gear set. High pinions went about 5 years. Both could be roached any time you wanted with big stickies.
There's 4 of them at my place, everything we drive has three pedals.
09 and 10 Tacoma 5 speeds are our DD's
07 5.9 Cummins 6 speed when it's needed
63 Chevy II SS 4 speed when I need my wallet to be thinner.