You think it would rather be something in the circuit?
Diagnosis whether it is a mechanical/capsule or electric/wiring problem is surprisingly simple and straight-forward:
Reverse the two wires that connect to the center of each diaphragm: switch and resolder the connection at the juncture where the yellow wires are soldered to the clear wires that disappear into the switch deck. Make sure to cover the diaphragms to prevent solder/flux splashes.
*If the dead side is now in front (in figure eight/omni patterns), it's most likely a wiring issue, and a simple ohm-meter test will reveal where the open connection is located.
* if the dead side remains in the rear (which is now the cardioid position), the problem lies with the capsule itself.
In either case, solving this is not rocket science - at reasonable cost, if any.