Hey Patrick,
Personally I wouldn't replace any seal unless it is leaking or you are already there doing something else (i.e. replacing the T-belt or water pump for the front seal and cam seal). Definately go with a Subaru T-stat. Too many others esp Stants are very unsuited to a Subie for some reason. Another place to try is Liberty Subaru in NJ. I've always had a good experience but was getting parts through Russ there long before anyone on the board was doing it. I'd go with someone here if I didn't already have a source that has treated me good.
Oh yeah, don't forget about that PCV valve while your at it. Again Subie is the best suited.