Warranty may be applicable, but it's not necessarily something they could have done wrong. Only way to really see if they did something incorrectly is to remove the locker and check the seals. Before that needs to be done though, there are some checks you should try first, or have them look into.
If it's the rear, check the rear diff breather and see if its plugged. If it is, replace that (and maybe consider relocating it, few threads around about it). Next you'll want to disconnect both sides of the air line (at the compressor/solenoid and also at the housing), then clean it to remove any oil inside it. I use brake clean and a little compressed air. After you're sure it's clean and dry, re-attach and then test it out. See if the problem still persists. If it does, you're looking at removing the diff and checking/changing the seals. I'd also verify the slider collar is able to slide back/forth freely with no interference when engaged/disengaged. It's also worth checking your rear axle seals for leaks as the pressure inside the diff will typically go through one of those if it can't go through the breather.
For the front, you're probably looking at the problem I believe I have. When the locker is engaged, you can potentially have positive air pressure in the diff. This depends on the condition of your seals for the sliding collar, and the connections/fittings for the air line. If you have said pressure, it needs to go somewhere, and like the rear diff, the front has a breather. Unlike the rear however, this breather is remotely located to the LHS fender. The problem lies in the routing. Generally, you want no horizontal spots in the path of travel. The stock routing has a couple of flat spots, and what I believe happens is oil gets trapped in these spots, essentially blocking the breather. So the oil needs to go somewhere else now with the pressure forcing it. Next is the axle seals. If those are bad, you'll leak out those (mine did, and I have replaced them but still have the problem). So the last place is through the seals when the positive air is released via the solenoid. I am in the process of relocating my front diff breather to eliminate the horizontal routing, but haven't had time to get around to it as the fitting for the breather hose on the front diff is unreachable (for me) with it installed. I'm hoping I can loosen the rear mount, remove the fronts and pry downwards (essentially rotating the diff even more) enough to reach my hand into the spot and remove said hose and attach my own.
If anyone else has insight on this problem I'm all ears, but this is where I am at currently.
