I have a numbers matching 68 firebird. Not show quality but in good condition. Super turbine 300 transmission was found to have some leaks. Well respected transmission shop that I was referred to wants to take out original transmission and put in a rebuilt turbo 350. He states superturbine 300s never worked well and he feels that repairing my transmission could be a waste of money as it may have issues in the future. He points out that the original transmission could be kept and, for instance, sold with the car in the future.

I would prefer to keep the car original if possible (some modifications would be needed for a new transmission) but I do see the benefit of having a more reliable transmission. Any thoughts about which would be more beneficial for resale in the future: a car with a rebuilt, more reliable transmission (that could be sold with the original transmission out of the car) paid for my me or keeping the original transmission on the car?

Any other thoughts on the situation described above?

I swapt out mine for a turbo 350 several years ago, it's nice to have that 3rd gear, but in a way I kinda wished I'd kept the two speed. Maybe if I get a wild hair, I might swap it back. That being said, do what you feel like doing, If you do make the change be sure to keep the two speed just in case
Good luck
Mark.........

If you are planning to keep and drive the car then upgrade and keep the 2sp for posterity. If you plan to get it running and sell then keep it original.