They still look good. I have seen worse…no teeth!
The part that is worn down on the left is the platform handle spline p/n 1030-129. It is now composed of a plastic material.
The part that is worn down on the right (part of the arm) is the handle head p/n 1030-084.
Remove the arm and you will need an Allen key to remove 3 screws p/n 04298 holding the platform handle spline. Along with it is a roll pin p/n 00506 which is a little difficult to remove. It’s best to get one – it is very cheap compared to the spline and the handle head.
If you ever break the Kipp lever (the little arm that you pull out to tighten the arm down) its p/n 09119 along with a washer and screw, if needed, p/n 04294 and p/n 08434, respectively. I’ve seen them get broken when the tripod/head is placed in a narrow case.
These parts should be available from a pro or broadcast camera shop.