Is it an FT, or an FTN? Is there an "N" above the meter window, near the rewind shaft?
You say it has "heavy brassing". Is it the black model?
There are several versions of the 55/3.5 with different values.
The alkaline cell you found is wrong, the voltage is too high (about 1.6v when fresh), which will lead to underexposure with that meter, and as the cell ages the voltage falls constantly, resulting in changine readings. It will be accurate for the brief period of time it delivers 1.35v