BIRD directional power sensors 4021/4022

[jfphp]

Hello,
Did anybody try to repair a model 4200 RF directional thruline power sensor from Bird ? The main board is fully closed with a black glue (tear ?). Is it just a box or, like a scope HV multiplier, does the black glue catch all the components ?
My 4022 has a funny malfunction : OK till 399 Mhz and from 400 Mhz (cal point) to 1 Ghz overload in FWD and full range on reflected. I guess it is a rom cal failure but how can I have a physical access to it (electronic access is possible with a 4029 calibrator but unobtainable...). Thank you.

[TheSteve]

I've repaired one but it was a simple power supply failure.
I also spent some time logging the com between the power sensor and the main unit as I thought it might be nice to make a custom unit that replaces the main unit but never got around to it.