I have a bathtub spout which needs to be changed out. When you pull up on the diverter to switch it to shower, 50% of the water goes up and 50% comes out of the spout.

I was told there are two kinds, one is threaded, and one uses a set screw. I am not sure how this one works.

Underneath the spout there is a disk with a flat head slot in it, but I can't get it to turn. I also can't get the spout to turn counter clockwise to unthread it.

This unit has been installed for at least 10 years if not more. I tried to research the unit, but all I know is that it's most likely a Kohler unit, since everything in the bathroom matches and the sink faucet caps say Kohler.

The tub spout has no name or model printed on it. The top of the diverter is stamped, and it reads:
PAT. 3086748. Other then that I can't find anything on this model.

I took a picture and if anyone can give me any suggestions it would be greatly appreciated.