The Bi-Post 'pins' on my Graphex full sync shutter; M - X - were not checking out as a good electrical contact. They looked dull and 'brownish'.
A quick clean with BRASSO made a world of difference! They are now conductive....and shiny, and near silver in appearance!

It's OK to clean them, but don't get carried away and polish them too much. They wear down normally, and you could hasten the process. Then, your flash cord won't fit tightly and the shutter will be due a trip to Fred Lustig for replacement of the contacts.

Thanks Alec, but I am NOT "Mr. Clean"!