What could cause the rear seal on my Toyota Tacoma's axle (same side) to go twice within a month?

I have a 2003 standard transmission Toyota Tacoma 2 WD truck. For a little while I had noticed a buildup of grease on the inside of my driver's side rear wheel and a burning oil smell. I called my local mechanic who just does tuneups, brakes + small stuff and he told me that it sounded like the rear seal and he recommended someone to go to. My wife and I had gone to this other person before and are happy with his work. Well 3 weeks ago today, I brought it in and had the rear seal and the bearings replaced for a little over $300.00. Checking around that is a fair price since there was 2.5 hours of labor. Well this past Friday I smelled that burning oil smell again for the first time since the problem was fixed. There was fresh grease on the wheel. I just got off of the phone with the guy who did the work and I am bringing it in tomorrow morning. Here is the question; Could it just be a faulty part (it is a genuine Toyota part) or could it be something else that is a bigger?What could cause the rear seal on my Toyota Tacoma's axle (same side) to go twice within a month?
Yes it could be a faulty seal. Another reason it might have started leaking again is actually common. If the mechanic was doing the work on the floor and using a floor jack to raise the back end of the truck off the floor to do the repairs and filled the axle that way it is easy to overfill. If the axle has been overfilled it will eventually leak out one or more of the seals. Another thing it could be is if your rear shoes were not replaced they could be soaked with lube. This could take a while to work its way out of the brake shoes but I don't really think this is it because you did not smell the burning for three weeks. Hope I have been helpful.What could cause the rear seal on my Toyota Tacoma's axle (same side) to go twice within a month?
Could be a faulty part, but if the same problem occurs I would contact the dealer of the truck and let them know what is going to. Could be a recall that needs to be started.What could cause the rear seal on my Toyota Tacoma's axle (same side) to go twice within a month?
One of the biggest problems of a seal leaking (the second time ) is faulty installation, improper seal driver, damaging the lip of the seal or just not being clean, another thing especially on a rear end is having a vent on the top of the axle plugged with mud or debris, it will cause undo pressure and seal issues.