Mine is a different brand from 1945 actually, but it acted as yours does when it got low on fluid. Even after I added some it took a few or more
cycles of the handle pumping to get it back, to purge the air out of
the system.

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85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson