I don't have the 53, but I can say can say the times I've used diff lock it's worked great. It was on stock wheels and tires though.
Since I've upgraded to mud tires and lighter weight rims I'm sure I'll end up breaking axles lif I use it much. Luckily I haven't needed it.
That being said, I was riding arguably the worst mud trails ever a few weeks ago and had a tire blow out. I rode on that flat for 2 hours with 4x4 on the entire time. I pushed the Z8 hard that night and nothing broke.
I know EPS can make it easy to break axles since you don't really gauge the bind you have your wheels in at times, in that sense it can be detrimental to you. Perhaps that could be it? I hope it's just a little bad luck you're going through.