The part that I was referring to is called a 1/4" Snubber Valve. Vision
Micro sells them for about $27.00.

When I did a google search for snubber valves I found that they can have a ball like check valve and their purpose is to dampen pressure fluctuations and fluid carried harmonics.  Arnie repeated the flight test (-1" MAP) with the same results (drop of 15-18 KIAS, -1.7 gph) but when keeping the MAP constant at WOT and dropping RPM by 100 his speed only dropped 2-3 Kts and .6 gph.  There is something definitely wrong with the path to the MAP sensor.  I guess we all have one of these since it is hidden inside of what looks like a brass fitting on the VM sensor block.  I will check mine the next time I pull my cowling.  If that is the problem, it would be a pain to clean it, easy to replace it.