The 129 was built by IH between Sep 1971 thru Oct 1974. They are very strong built tractors.
Since these tractors are 35+ years old, it would be prudent to expect some repairs. The amount of repairs depends on who owned it in it's life and the level of care and maintenance that was given to it.
You can't buy a GT today with a solid frame, cast iron rear end and front axle. The Kohler K series motors are a true work horse .....tried and true.
Parts are still available for both the tractor and motor.