Punch - I took a look in my early Chevy resource books. Although I don't have a 1935 Shop Manual, the 1938 Chevy Shop Manual provided the below diagram of the front u-joint and drive ball assembly for 1938 1-1/2 ton trucks, which I think is the same design as your 1935. My 1929-39 Chevy Master Parts Book info matches the shop manual info.
The "cork gasket" (seal) is circled in red in the diagram, compressed against the ball by the ball retainer. Hopefully others with your earlier 1935 truck can confirm that this information is correct.
