I recommend KONTAKT 60 - a typical application is cleaning tarnished contacts. If you want to comprehensively preserve the contacts, then:
KONTAKT 60 dissolves the corroded layer,
KONTAKT 61 degreases and washes away residues
CONTACT WL leaves a protective layer on the contacts.
You can buy it in the WW.SMARUJ.PL online store. Various packaging.
The picture below shows the instructions for cleaning the contacts according to the Kontakt Chemie catalog
here shortcut to that directory