single keypress randomly registers as multiple

[Special K]

I have a Filco Majestouch 1 (Cherry MX blues) bought new in 2009 that has developed the following issue: the '6' key will randomly register multiple keypresses (usually 2-4) when it is pressed once. This issue occurs about a third of the time the key is pressed.

I've completely disassembled the board and cleaned it and also sprayed some canned air into the 6's blue switch with the switch partially pressed down but the issue persists.

Is there any way to fix this short of buying a new keyboard or soldering gear + a new cherry MX blue switch?

Aren't these switches supposed to last for tens of millions of cycles? This keyboard has been my daily driver since I bought it but prior to COVID it didn't see heavy use.

[Findecanor]

One common source of chattering is a bad solder joint.
If you have a soldering iron, reflow the switch's solder joints. i.e. for each one, heat it until you see that the solder melts and then let it cool again.

If that does not fix the problem, the problem could be a defective switch.