canonball
Without being totally familiar with the solenoid.. I can say confidently that the solenoids of the time (Correct me if I am wrong. ) were a metal bracket riveted to "a body ", be that metal or plastic /Bakelite.
Which ever ~ in a starter solenoid there is a "pull in" coil, and a"holding coil" ~ the first pulls a metal plunger, thus closing the contacts, a second coil takes over and 'holds ' the plunger and contacts as the primary coil draws a lot more current .
These little buggers DO ~ over years build up moisture and corrosion which may well account for smoke and erratic performance, and even smoke, after all , given it is the original unit it is getting on .
Personally . I know they can be serviced, with some effort. but simply put it probably easier and more effective to simply replace the unit .
As the other bloke's posts suggest , there are a number of possibilities, but ~
One effective simple test this a test lamp will give some insight.. by activating the starter and holding the test lamp of the first battery cable post and then the second, IF you're having solenoid 'resistance' problems the test lamp can very well show a notable difference in brilliance which will indicate contact deterioration !
8)