Now I KNOW they're not that big - 25mm is almost an inch! These are in the 3/8" range, and that makes them 3/8" or M10, and I remember them having a coarse thread.
I don't have any handy that I could measure, but I'm willing to bet on 3/8"-16x1.25", or M10x1.5x30mm. Both should be relatively inexpensive and quite readily available (by contrast, that M25 the dealership is trying to foist off on you is slightly smaller than the output shaft on your transfer case....)
5-90