Problem with DG

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?

Is the DG grinding? What does it sound like at shut down? Especialy when it gets to the end of winding down?

I do not recall any abnormal sounds when it is working (Can't hear much in an Apache). It seems to spin down normally when it's working. I don't think it spins up when it doesn't work - I will pay more attention next time.

After engine shut down, Listen to the gyro all the way to the end of it's spool down. Hear what it sounds like. Is it abrupt, grind, smooth, ? I had a aviation scrap yard at one time and it doesn't take long for a gyro to go bad. We had a rig to spool them up so the bearings wouldn't go bad and to listen to for noise before we shipped them out so they wouldn't come back. Any grinding and we sold it as a core.

rv8505, just curious where you can sell a gyro core? thanks, turbo

Thanks. I will have some time tomorrow to check it out.