I had/have the same issue with an L2M. Lost all high frequency, but it was somewhat intermittent. It got sent off to L6 for repair and came back no fault found. It seemed to work OK so I carried on using it until it happened again. It is out of warranty now; this all happened over a year ago. Partially my fault for not being more persistent I suppose but at the time I had other things going on that were somewhat more important. It annoyed me that it was just sent back without finding and fixing the fault.