Okay, I removed the metal tubing to inspect the check valve. There does not appear to be any sign of a check valve. The piece connected to the pump has absolutely nothing in it, the same basic diameter as the tubing. Looking into the vacuum pump itself I could not see anything. So now what? Have check valve bits been sucked into the pump and is that causing the intermittent vacuum pressure. Does the check valve reduce the vacuum pressure as well as prevent leak down? If that is the case wouldn't my vacuum pressure be a lot higher than 21 hg? So is the next logical step to replace or rebuild the vacuum pump?