The last straw for me with the '72 Yamaha TX 750 was finding out I needed Yamaha special tool xxx to break the cam chain before the top end could be taken apart to fix Some of the oil leaks, and Yamaha special tool yyy to rivet it back together. 
I bought a chain breaker/rivet tool for my TX(74' TX500A 180 degree crank,dohc and 8-valve two-piece cyl. head)back in the early 90's which did both chain breaking and riveting the new link back together;the name of the tool manufacturer was Kent Moore.
I imagine you needed a different tool for the 750.
I sold my TX after a couple years and having done a top-end freshen-up 12,000 miles prior and didn't even need to replace the balance chain,although I was at the end of the adjustment and it was ok at that point.
I've heard horror stories about the TX750's 'Omni-Phase' balancers/chains..
The TX500A ran rode very good for me.
