[Collins] How to clean 7, 9 pin metal ring?

[Yong Surk Lee/HL1FB]

Hello; 
A friend of mine is cleaning a very old and dirty Collins KWM-2. 
He was able to clean the chassis with a cleaner named PB-1 which 
gave excellent result. However he was not able to do anything with 
corroded or rusted metal rings of 7 and 9 pin tube sockets. 
The best way seems to be replacing the ring but it is not easy. 
We are thinking of using some chemical to remove the rust and coat them 
with somekind of transparent coating. 
Anybody has experience with this? 
de WW6N