NavList:

Hi, I don't know very much about the MA-1.  Your light path analysis is well beyond my investigations, however, if you are looking for silicon fluid, it can be found at Midwest Lubricants (they have a web site (https://midwestlubricants.com/) and sell silicon fluid in a variety of viscosities.  I was not able to find 7cst, but they do have 5 and 10.

I also do not know how one fills an MA-1 chamber with fluid, but the MA-2 (Kollsman bubble) repair manual has a fairly involved procedure to fill its bubble chamber including connecting to various ports and using differential temperatures to get the fluid into the chamber.  A few of us here have found that the repair manual doesn't have to be followed to fill the chamber enough to get a usable bubble.  Not suggesting that would work for your MA-1 but it's a datapoint.