Looks like there has been a critter of some kind all over the RX input.
The UR-FR5000 has vent slots above the fan cut into the lid. These needs to be cut into the lid.
After carefull cleaning the repeater will receive down to -120dBm and no parts required replacing.
Scope is showing audio signal on "AFOUT" on the DB25 (pin 22).
Signal Generator is outputting on 434.95MHz (RX frequency), and the RSSI level on the board changes appropriately as the Signal Generatior output in modified. Fails to receive if I move it off frequency, so selectivity seems good. I'm TXing into a load, without that it wasn't too happy.
I did find some of the RF transformers in the mixer had dodgy insulation where they "crossed over" the windings. I insulated them with a sliver of kapton tape, also one of the windings had broken off the leg, but that might have been me when I was cleaning it all with a brush and isopropyl.