I just replaced mine today with the ones from my '97 parts truck. One had some thick grease on it, it seemed like when the axle turned, the cams couldn't compress the hub enough for it to engage. When I replaced that one, the passenger side one finally started getting some torque and it made a horrible buzzing/grinding noise, so I replaced that one also. The parts that were on the axle shafts looked in fine shape.
I put the bad ones back on the parts truck for now, will probably take them off before I junk it, maybe take them all apart to see how they work. I think the one might be fixable with a good cleaning, the other one I'm not so sure. At some point, (not anytime soon) I think I'll try to take one completely apart, that info on TRS is ok, but I like big pictures and detailed service steps.
I can see where excess grease can limit the functionality of the locking, especially if it gets like one of mine where it is really thick, almost kinda dry, but I think a token amount of grease, a very light coating on the axle shaft parts wouldn't be a problem. Just not gobs of it. Not packed like a wheel bearing