[Yosemite Sam]

Welcome to OCC, You have chosen a fantastic hobby, I can see that in short order you will have yellow fever and be overrun with Cub Cadets.

It really depends on what has been done to the machine and what you think it needs.

If the engine runs well and doesn't smoke or leak oil I would leave it alone.

Weather you do any work to it or not, while the engine is out, I would remove the front PTO, clean up the bore (where the bearing goes) and the set screw holes. Then put a little anti-seize in the bore and on the new set screws. This would be, just to make it easier to remove when the time comes for a pto rebuild.

If the steering is loose or sloppy I would rebuild the column, replace the tie rod ends and bend the axle saddle back into shape so the axle isn't sloppy.

If you are going to have the tractor apart, I would rebuild/replace the clutch and drive shaft, primarily because having it out already is half the battle.

While the trans-axle is out I would seriously consider removing the covers (top and rear) and the axle tubes. Then wash everything out and replace the gaskets, axle seals and axle bearings. Also check the input shaft bearing on the front of the trans-axle.

The only other thing that comes to mind is replacing every spiral pin in the machine, they are inexpensive and much easier to replace while you have it apart.

It sounds like the PO/s have taken pretty good care of your 124 so it may not really need any of the above mentioned repairs, the things listed are just normal wear areas that are often times in need of service. The things that the other guys have listed are also good ideas.

If you do make the above mentioned repairs you should end up with a machine that will give you a good many years of service and help to make a lifetime of memories for your kids.

Good luck with your project.