Past experience indicated that the only reasonable cost effective way of overhauling transmissions with minimum cost, was to acquire a number of scrapped units, then strip, inspect, then cannibalise, assuming the required components were not shot.
Regular practice on the old Rootes transverse axles we did, but when I had the layshaft needle rollers collapse on a 3.3 GM box, the breaker was the cheapest way forward, as new components were prohibitively expensive. In your case though, maybe a few relatively simple bits may sort it. Good Luck.

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