In general, the QuadRange is a great tranny.  If it is truly grinding, then the previous owner might have regularly tried to shift the ABCD lever while in motion. (?)  I never move the ABCD lever unless I am stopped, and have idled-down.  Quiz him about how he drives it, and shifts it..

The JD 40 series tractor were great...in my opinion are still great.  I think it will make a great tractor for you.  You probably ought to change the trans-hyd. oil and the filter(s).  Keep the front pivot greased like grease is free.  Grease, but don't over-grease the rear axles.  If the tires are scooted all the way in, and the rear axle zerks are hard to get to, you might question the owner how often (and how much) he greased them.  You may want to put the grease lines going to those zerks if they're hard to reach.  It could make the difference in the axles lasting--or not lasting..Chances are if things are good, then the owner has been doing things right.  On my 4440, we put the grease lines going to the rear axles, and have the zerks real close to the SCV's....very easy to service them.

Other than a head gasket, we have not done any work to our 4440.  I recently put an interior kit in my tractor, and a new seat, and painted the exterior...Now she looks as good as she runs !! I have no plans of getting rid of my '40 series any time soon.  If it is a sound tractor, I think it would do good for you.