When I purchased my 1924 Buick, the line in the Motometer was red all the way to the top. So, I started reading on this an other forums about how to repair it. Somewhere in one of the forums, someone said to spin it in a bicycle wheel. I don't know who said it but it worked!
I flipped the bike upside down, put it on a table and secured the Motometer between the spikes, head towards the rim, and started spinning. After about 1/2 a mile, I stopped - there was no change. I figured I would give it another chance and I spun it for about another 1/2 mile and a higher speed. This time when I stopped, I saw one tiny bubble, that was not there before, in the bottom of the glass tube - maybe success? So I stated cranking again, left hand then right. At the next stop, there were 3 bubbles! More cranking at as high a speed as I could crank, Lance Armstrong would be proud, and there was one large bubble close to the top. More cranking, and success! All of the red was at the bottom and the top was clear. It only took 7 or 8 miles, but it worked.
I have driven the car several times since then and the Motometer moves as it should.
So, a big thanks to whoever made that suggestion.