mine cycles about once about every hour with the locker disengaged. Never had the locker engaged for more than 5 minutes, and it didn't cycle. FYI I have the small compressor.
I would build a test jig like it says in the instructions, or like ZUK has, and test the locker itself. Since Marlin built it I would assume that its good, and for your sake I hope that it is. It would be much much easier to fix a leak in the air lines/fittings than to yank the diff and re-do the o-rings
my .02
PZ
