Well...... one can never be real sure without having done some tests - otherwise it is an educated guess at best. Tests? Like line pressure in various gears, maybe bolt on an air test plate in lieu of the valve body and test, etc things I am sure that probably were not done in your case.
Without casting any aspersions at all, my guess is that once he saw the list of possibles, the only one that would require removal was the reverse clutch, and so he settled on THAT as the culprit. Most typical shop mechanics know little about the internal workings of automatic transmissions - leaving those to persons trained on them, and who do mainly automatic transmission rebuild work. It may well be correct, but I would have some trouble believing that he could say with certainty that IS the problem. Would have at least been nice to try some of the other things...ah, the beauty of doing your own work!
BTW...How many miles on the transmission? Have the filter or fluid even been changed?
I will point out that you could have run up a few hundred dollars of shop time to have run down that list, and possibly not solved anything, in which case you'd just have blown that money on TOP on the rebuild.
As I listen to people report their experiences on here, more and more I sense that when people have ANY sort of automatic transmission problem, the usual response (almost a knee jerk really) is "It needs a total rebuild". While that may be true in a lot (maybe most) of the cases, I doubt it's true in every case. Yet, if you are running a shop, you could putz half a day trying to repair an automatic transmission, only to end up telling the customer it needs a rebuild... you are likely to have a customer who is unhappy that you want to charge them extra for the time you spent putzing on it. I can hear a customer saying "Geeze, why didn't you just tell me right off it needed to be rebuilt!" So, there are two sides on most everything.
Let us know what you find out.
