I have a vacuum driven DG in my 57 Apache. I have vacuum pumps on each engine. Recently, my DG has been intermittment. My IA says he has never heard of an intermittment DG - they work or they don't. He said to double check to ensure it is uncaged. I did and it is. But on the last 4 (VFR) flights, it worked, it didn't, it worked, and then it didn't. I am hesitant to file IFR (actually delayed trips) until I am confident that it will work.
Anyone experienced this? Any clues to start trouble shooting?