The car levels frequently with no change in load. It wears the battery down. My mechanic checked the entire system for leaks and replaced a lot of tubing, but found that the check valve leaks. He could not find a replacement. He tried rebuilding the valve, used carburator seals, and it seemed to work for a while, but the repair is not holding.

Is this part available or do I hit the boneyards and hope for the best? I've pulled the fuse to prevent killing the battery again.

Thanks for your help!

Try www.rockauto.com . Other than eBay or a junkyard, there isn't much else! That's the problem with a Cadillac that old, no one makes the expensive high tech parts in the aftermarket, and GM stops making parts for it's cars after 10 years.