Dang, those secondaries got expensive. I think I paid less than $200 for the last one I bought and that wasn't all that long ago, maybe 5 years.
Again, those primaries really don't have a lot to them inside. Pretty much just a spring and some clutch weights. A parts manual is located here which will have a nice schematic:
https://www.buggiesgonewild.com/colu...MP_SHUTTLE.pdf
Those come apart pretty easily. You may want to do that and clean everything out really good. There is a sizable spring in there too that you can replace. Most of the other stuff is what it is, though.....stuff that really doesn't wear out. Check your flange faces to make sure that there are no grooves on them or anything.
Oh, you probably did this but make sure that you have the right belt. If your belt is even an inch bigger than it's supposed to be then your secondary won't open as it should. You may want to get one from a reputable seller as a lot of places will ship you a Harley belt and tell you it's for a Columbia. Kraft Implement in Wisconsin or Vintage Golf Cart Parts in Washington will send you the right one for sure.