DeOxit or any cleaner can only be a temporary solution to noisy pots, any contact or switch cleaner should be used sparingly. In this case, the effects loop is two switches and the contacts can only really be accessed from within the case.
For switches or switching jacks, I recommend a standard switch or contact cleaner, which is both cheaper and probably more effective. The other option, although not ideal, is to install a patch cable into the EFX loop, although even those contacts may corrode over time.