bent valves on all cylinders

Dear Uli Hofer,

Yes tell us the final diagnostic.

Thanks in advance

A slightly different issue that may be related:  My 912UL sat unused through the winter and spring.  Burping the oil caused a gurgling sound to come through the exhaust - removed the valve covers and noted that all of the valves seemed to function properly - would this sound be a symptom of a vent valve stem?