Recently I wanted to clean full banks of relays and switch stacks on an EM without pulling every relay apart. I used an Electrolux steaming unit which removes all the grime and works a treat. You will need to ensure that you thoroughly dry off any excess moisture on parts with compressed air or leave out in the sun.

Interesting - I thought the steam cleaners leave a damp residue ? In the case of relays on the baseboard, doesn't it leave steam / water on the wood etc ?