If you have a power-shift problem a 70 series is not toast.
The only time I had problems with my 1370 was after I changed oil to something other than HyTran.
I was told brand X oil was equal to Hytran and its is not. In my case I did spend a lot of money but only because Brand X oil dissolved the glue from the Disc's on the tractor including the brakes.
I know of a yellow 970 that had 16,000 hrs that began to have a little shifting trouble so instead of cleaning the spools or trying to find out the problem thee owner ground the spools down .030 on a lathe.
Needless to say their 970 died. So the biggest problem I see with 70 series tractor is people (like me) using the wrong oil or doing something well, not to the best interest of the tractor.
I would not be afraid of a 1070 or 970 if everything is ok when you buy it.
Just my opinion