Others on here will know more but from my own recent investigations (see elsewhere also on here) the calibrator signal at that strength would appear to rule out the usual suspects of faulty RF/IF amplification devices (3SK51, J310 etc).? I bought my 101Z new 41 years ago and it has been a fantastic piece of equipment.? I have been looking for another one for some time now but with no success...? As and when you find out the nature of the fault I (and no doubt others) would be pleased to know what it was, how you identified it and how you rectified it.? Good luck.
Alistair GM4ENF
Alistair GM4ENF