how do you know which of the two ADF signals which may be displayed in that indicator is faulty, what specifically does your ops manual say about this situation...?
There are three flags in each RMI...two signal condition flags, and one PWR flag.
If the RMI fails, the PWR OFF flag appears.
If the VOR receiver should fail or the VOR not be operable on the ground, the respective fail flag will appear, if VOR is selected.
If reversed sensing (IE, 180 degree ambiguity) is sensed, the respective fail flag will appear, if ADF is selected.
If the ADF transmitter on the ground should fail, a fail flag will not appear in the RMI, so audio monitoring is needed. In addition, on some installations, the ADF needles will be driven to the nine o'clock position.
If the ADF receiver fails, the respective fail flag will appear if ADF is selected.
I know you "only fly 'em" but is it possible you could ask one of your "highly experienced, long retired, manufacturer trained" hot shots to explain it to you and then you can come back here and tell us all about it...?
If I remember, will do.
Keep in mind these folks didn't design the system, they only fix it when necessary.