I've searched in all of the other Subaru sites that I belong to, for my previous Subaru technical links about this subject, but with no luck.
And yes 1 psi, especially at the rear creates a push from one side versus the other through the RLSD. Fortunately, I check my pressures every week, or at least every other week now that I'm driving less, so I typically catch any changes before it affects the handling.
WRT your TPes, sounds like your rims or your valve stem(s) may be leaking. I had a set of AM rims that leaked like a sieve - turns out the metal was too porous. Changed out all four valve stems, still leaked. Finally spray-lacquered the entire inside of each wheel and that fixed the issue. No more leak-down.
Pro dilectione Dei et patriam