Agree with Mark, the TX has been unfairly branded as a lemon. There were early problems with the design but Yamaha got them sorted with mods, and shipped some complete modded engines under warranty. These are identified by having no engine number stamped into them, like mine. Deep sump, adjustable balancer chain, various improved seals, are all in the modded engine but can but retrofitted to other engines. Modern synthetic oil alone will probably be enough to keep them together.
Vastly under-rated bike and consequently quite cheap. Almost unknown here in the UK but still seem to be plenty around in the US and a few in Europe. The XS650 is a good bike, but the TX750 makes 20% more power and 25% more torque for just 90cc more, and at lower revs too. The TX will stomp a CB750 in a top gear roll on, anyday. 50-60 miles per gallon (UK), 110 mph, twin discs as standard or option, 19 litre tank for 200+ mile range, sounds like a Norton Commando, and a real looker. Many parts still available except standard silencers, which are hen's teeth. Mine is a '73 in Candy Gold Metalflake with European-spec low bars and big tank. I've done 3500 miles with no complaints.