This comment should bring up some memories, I too think it is a remote brake reservoir. It did remind me of a bottle for alcohol injection for air brake systems, in freezing weather without the use of an air dryer you had to keep the condensation in the air tanks and lines ice free.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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