The legacy bearings are sealed units the Impreza one's are not.
Last time I had mine done (3rd time) they said the was a TSB and had used different spindles to cure the problem.
to save money you can get the parts from NAPA
Legacy 4wd rear wheel bearing:
- subaru part #: 28016AA030 - $100
- napa part #: GRW175 - $37
(both are NTN 4T-CR1-08A05 bearings)
It's actually pretty easy to get your rear knuckle out, then just take it to a shop and have them press the hub and old bearing out, then press in the new bearing. Then re-pack the bearing with waterproof grease and install.
You could probably do the whole thing for $150.