[kens]

The IBM 1401 team analyzed the gold on the SMS card edge connectors and found they have 100 microinches of gold, which is a lot by modern standards: http://ibm-1401.info/SMS_Tabs_IBM_Report_Dec2007.pdf

The connectors were generally reliable; I don't think we've had any problems with them. You could clean them with isopropyl alcohol if necessary. There was one IBM manual that described a process for removing SMS cards where you'd put a punch card on either side of the board to protect the board against catching on neighboring boards, and then use a special puller to remove the board. But we just pull the boards out by hand without problems.