My Subie: '94 Legacy Ti, AWD, manual transmission.
At around 135K mi. my transmission started to refuse to stay in 4th. It would occasionally pop out of gear, especially when decelerating. Predictably the problem got worse and I bit the bullet and swapped in a "new" transmission. Unfortunately I didn't bit the bullet hard enough. I opted, due to time and money constraints, to use a salvaged transmission. I have no idea how many miles were on this replacement tranny but I got it in (with a new clutch and half axles) and a lot of cursing.
Everything seemed fine until now, about a year and a half or 10K miles later. My first undesirable symptom was difficulty getting into 2nd. It felt like it wouldn't get into gear all the way or sometimes it would just feel blocked. Don't know if it was just me figuring out the nuances of the difficulty or what, but that problem resolved itself. It has now been replaced by the original problem. Won't stay in 4th.
Ok, I'm getting to the point of my question. I cracked the old transmission and found a severely worn main shaft bearing and the rear thrust bearing had about an 1/8 inch groove worn in it. I've replaced those and I'm waiting to get the motivation to swap it back in (read: waiting for the current situation to devolve into an undrivable condition). What I'm wondering is Did I do something wrong? I mean, I know I should have done the original replacement with a rebuilt or new tranny. But now I've gone through two transmissions, only one of which I installed, and I'm wondering why. Is it my driving? Did I just get unlucky? Is there a chronic problem with my or all subies of this vintage?
I've searched and read through this group (love what I've learned so far) but can find no satisfactory answer. I hope someone out there has an answer or at least some junk science to throw my way. Thanks.
-Max
PS: Where is the viscous coupler differential? I've been in the transmission and it didn't jump out at me.