In our 2000 328 the driver's seat doesn't heat any more. The passenger seat is fine. When you switch the driver seat heater switch on, it flickers momentarily; otherwise, nothing happens. So obviously the fuse is good, and power is making it to the switch, but I'm thinking there is either a fault in the heater, it's not connected, or the switch has a problem. Any advise on troubleshooting this?