[Boatanchors] Old toggle switches question

[hwhall at compuserve.com]

 The 40's vintage Link electronics I'm helping restore has some old round-headed-bat toggle switches (hard to find modern matches) that are a bit flaky in making good contact. I noticed what looks like tar-filled holes on the backside of some of the switch bodies. I'm thinking I can clear that and clean up the contacts. But I don't want to start hacking at the switch unless it really is simply a filled hole that can be refilled. 

Has anyone seen switches like that before? Or tried to open & service them?


Thanks!

Wayne
WB4OGM