I have a GC4 with K55 profile rubber installed by Pat Sheehan in Portland about 15 years ago. i've been getting some ball bounce off certain places of the cushions. A few inches inside the corners on both short rails and also the same near my side pockets. Rail height is 1 7/16, checked a few times. Shimmed the worst spot yesterday and thought i was good but it's doing it again today. Could i get some suggestions as to a cause? I would assume it's a cushion thing but what? Rubber getting old? Glue? Why in just those spots?