Everybody has some ideas on this subject and you probably won't get a straight answer from anybody. But here's my idea. I believe the sticking on the early clutches was caused by mis machining of the center shaft or the bushing on the primary clutch , get it hot and it sticks you could here it "click" loose when it released. Now add some belt dust and it gets even worse. Let them sit outside at the dealer and drive back and forth 20' to put them away every night with the clutch moving very little and the problem compiles.
These types of clutches on all machines(snowmobiles, utvs,etc) are prone to sticking if not kept clean.
as for the "FIX" it varies like you already know. Soak the clutch in a good bubble bath then blow it out reassemble and try it. If that doesn't work try cleaning up some of the metal with some emery cloth like some have done. You can try a primary spring also. And if all else fails you will probably have to get a clutch.
the clutches have the same part number I believe it was a quality control issue that slipped a bunch of these into machines.
most brands have had issues with clutchs at some time. Be patient and methodical with your diagnosising and your fixes and you'll have it figured out in no time.