manual trans only has one speed sensor. and i think it is on the driver side. but i'm not a MT kind of guy. they may still call it VSS2 not sure.the auto trans has 2 so it can compare front wheel speed to rear wheel speed for the AWD. the 5 speed AWD so 100% mechanical so only one VSS.
a used subaru alternator is a better choice, imho, than a reman from the parts stores. measure the voltage at the alt and the battery and compare. there is also a subaru reman from the dealer for 98 outbacks, i think. the stock units had a recall, so subaru reman-ed a lot of them. much better quality than the parts store.
FYI: the battery starts the car. the alt makes the electricity that the car needs to run. (if the alt does not supply enough power the car will use the battery to run the car.) as the demand for power increases, head lights on, so does the alt output. if your battery has a bad cell, the alt can over charge or ''cook'' the other 5 cells trying to fill the demand for power. or the alt can be weak and not generate enough power as it should. but the common fail point, if not bearings in the alt, is for the diodes to fail and the alt does not generate / regulate correctly. some times too much, some times too little.