A well known (and expensive) contact enhancer is a product called Stabilant 22. I have bought it at Carquest stores (unfortunately they renumber it and I don't remember the number).
The concept behind its use has to do with the microscopic surface of contacts. They are actually not smooth; but full of peaks and valleys. The product fills the valleys with a conductive coating.
Its greatest use is in low voltage computer connections.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician