hello, thought id share my experience in here. i own and work on mostly subarus in alaska,
i have used belts on my car, almost always do. 258k miles on it had it from 142k . 3 belts from there to now and im hard on that car.
reason i use used belts is i work on a lot of subarus . have a wall full of used belts.
distributor can break the belt. the bearing set in it can be bad and not show tell its hot. long drives or long idle periods. also seen them lock up in cold conditions. 10F or colder.
if the belt is not installed right, slap allowed will tear teeth off. so will dumping the clutch at a high rpm.
how to you drive your car? like a law abiding citizen or watch this an hold my beer?
oil pumps can also creat a lot of drag although this is much rarer of a issue
also how are you installing that belt? use the single idler gear with the one 14mm bolt to get belt back on. if you slip it on with force you could be damaging a tooth and helping the ware right along.
and the no cover is a terrible idea. dabre bouncing around the bay could end up in the belt set. seen that many times