The thing that causes recurring problems is re-installing bad parts. The bad part in this case could be the shift shaft itself. I check every one for scoring caused by grit embedded into the seal. You can get a taller seal if needed. At this point, I'd check the end play by pulling in and out on the input shaft. I know lots of readers are shaking their heads, saying you got the hard part done, now crack that bad boy open and just replace what's necessary; (going out soon). They usually have wear in the front drum (direct drum or 3rd gear drum, or reverse/high drum) lots of names. The next one back is the forward drum; even tho it's not in the most forward part of the trans... Any wear inside these two drums will doom your trans soon, so it's worth it to pop the pump and check the clutch surfaces in these two drums...also the band condition, but it will probably be fine..
