Triumph Repair: tr-6 overdrive, clutch pressure plate, factory option

Question
Scott, There is a TR-6 on Ebay that has some transmission issues. I'm interested in this car and owner says "Once warmed up the car will not down shift into Second gear and at times difficult in getting into third". Also the overdrive will not engage with owner stating it needs the solenoid replaced. I'm interested in knowing if the overdrive for a 76 tr-6 is just an add on and the basic transmission is generic?  Solenoid replacement is fairly straight forward but if I have to crack the transcase I might as well rebuild the tranny?  Your thoughts please.

Answer
Solenoid may be the issue, may not.  You wouldn't know for sure until you replaced it, and saw whether it worked or not.  OD was a factory option on TR6's.  It is a different tailshaft housing (big bulb vs. skinny cone).

Then 2nd/3rd gear issue sounds like worn out synchros, which would necessitate a rebuild.  

If bought, I would plan on worst case of rebuilding the transmission and the over-drive, and doing the clutch/pressure plate/throw out bearing while you are in there.  You can search the internet for those companies that rebuild these trannies, and get an estimate, but I believe you are looking at the $1500 range to rebuild an OD tranny.