Walter, getting back to the TX500, it lasted about 4-5 years being renamed the XS500 in '75. It was the TX750 that had the counterbalancer issues SOHC head and only lasted 2 years.
I owned a TX500 and it was an okay mid sized bike, very pretty blue/purple color. Bought if from a rich kid for $125 after he dropped it. I rode it from 78 in college thru to 86. The only problem I had was a starter clutch that went south which required kick starting all the time. Took about 100 kicks in the spring after a winter sleep. I never changed the oil filter on that bike and could only drain 1/4 the oil out per change because one of the drain plugs was replaced w/o a washer and siezed in place. Ran like a top w/ very little vibration. Flat power curve, no hit at all.
Anyway, it was a bit of a disapointment in that it was really hi-tech with electric start and DOHC 4 valve head, but it was rather slow. My friends old SOHC Honda 450 was faster and the Honda 750 would eat it up. I rode with a guy on a new CB900f so just I couldn't keep up.