I have a TRB5 and TRB6, both Mk1 made in Japan. Great instruments.but slightly noisy preamps, though nothing to worry about in a live setting. Had a MkII TRB5 for a while but didn't get on with it, not sure if it was the 35" scale or just general tone/feel.
The cutaway on the Mk1's that is supposedly there to help popping etc. I find a bit annoying, as the gap under the top strings is too big compared with my other basses. It's a fix for a problem that never existed imho.
Yes, the jack sockets are notoriously unreliable - I think I've replaced them on all my 3 Yamahas at one point or another. I also wax-dipped the pick-ups on the TRB5 as I found them a bit on the microphonic side.