It is most common for the motor adjustable varidisc to wear out and start to rattle. Be aware that the original ones had thin black plastic inserts glued in. Later ones and current production uses a green material that is a lot thicker and wears a lot better. But the green versions are not repairable. They are only replaced. Note that there were two different HP motors and they had different diameter shafts. Therefore order the correct parts. The front varidisc is common to all, and still has the thin black plastic inserts glued in. There is a lot to get correct if you try and glue in new inserts. The varidiscs cannot wobble and must run true or you will have vibration issues. If the plastic inserts wear out, they will destroy the shaft, so it is crucial to replace the varidiscs before that happens. When I rebuild a head for a customer, I have to use new parts, as I guarantee my work. Also I usually replace the 3 top bearings and replace the vari-drive belt. This ensures that I will not be turning in the near furure and the customer is well taken care of.
By the way. A "J" head refers to the step pulley head. The vari-drive head is referred to as a "2J' head.
The boottom end may be worn out or not. You will be the judge of how much play you can tolerate. The ways may or may not be chromed. If chromed, it complicates a rescrape. Most way surfaces get dished or worn in the center. A new gib will not help. Be aware that gibs are ordered raw. they are not fitted and lack oil grooves. That is an additional cost. Check the backlash, that is a rather easy adjustment or you can replace the brass nuts. Be aware that just like the way surfaces, the screws wear in the center first. If you take the backlash out of the center, you may not be able to reach the ends of travel.