[R-390] Cleaning sub-chassis

[richard may]

Wonder if anybody can give me some tips on cleaning an R-390A sub-chassis. I want to clean a crystal osc module. I think if I remove the oven cover, the T-207 cover and remove the crystals, I can give this thing a bath. I remember reading somewhere how this is done but can't find the article. The inside is pristine but the outside is really dirty.  Any tips? Richard, W8FCW