The power top of my 97 993 C2 Cab (37,000 miles, excellent condition) has stopped responding to the dash switch. New drive cables and gears installed and syncronized at Porsche dealer last summer. Worked fine until early this summer then became erratic, working sometimes, sometimes not. Now no response to dash switch. I switched out the relay, with matching relay that I know is working, to no avail. Car stored in garage, driven infrequently, perhaps 500 miles since power top repairs. Suggestions?