Something is expanding when it gets warm. It might be the throw out bearing. Pull the inspection cover. Measure as well as you can the clearance between the presser plate fingers and the throw out bearing. Long feeler will get you close. Drive it until it starts acting up, slip under and see if that has changed. I have seen the bolts on the presser plate strip and release the plate. Just a bit, when cold the plate is flat and straight to the fly wheel. When warm the plate is warped. The pivot ball might effect the adjustment? 0.3 inch is not a lot but maybe. It should not change as it gets warm, unless the pivot is loose, or the retainer spring is broken, that might do it. That is all i have at this time, maybe some one smarter will speak up.
