If the breather is clogged, I would think that it would leak out of both sides, not just one side, but who knows? To test the breather, just unscrew it and blow through it. If air comes out, then it's fine. If not, then it's clogged. I think a new one costs about $7 (or was it $15?).
To change the wheel bearing, you'll need to also replace the wheel bearing retainer, which can be difficult to remove without a press. Whatever you do, don't torch off the retainer unless you have no other choice. The heat will cause the steel molecules to expand, making it difficult if not impossible to re-install the axle back in the diff carrier (I speak from experience - I had to lay the axle in ice overnight to get the steel to contract so it would go back in).
One other thing to check is the O-ring that goes on the end of the axle around where the rear axle seal goes. It's often overlooked when changing the rear axle seal because it's hard to see. But old ones can still be re-used if they're still good. Even so, I don't know if a bad one would cause a leak, but who knows?
Unfortunately, I don't remember how much the wheel bearings were when I changed mine. I think I got them at NAPA, though. You might want to check Chris and Barb and TRDPARTS4U.com for them - they're OEM and are probably cheaper than the NAPA ones.
Hope this helps.
