Ha ha ..... I was waiting to see what your reply would be, Mr Candles.
My initial thoughts too, are that it is a port/line card fault ........ taking everything into consideration about what has been said ??.
You may (or may not ??), remember from your halcyon days in the Exchange, that port/card issues are the remit of the OMC (Operation Maintenance Centre), not we front-line engineers.
Don't get me wrong, if we find a faulty port 'on the day', then we will contact the OMC and have them allocate a new port, to which we will just re-jumper on the MDF .............. but regarding a 'monitoring system' I haven't got the foggiest idea, as it has never, ever been something 'outside engineers' have been privy to ??
A simple RAT (Remote Access Test) on BT classic circuits will generally pick up faulty exchange equipment ..... however, we don't know if the OP is LLU at this point ?? If they are, then it introduces another possibility into the fray ...... TAMS equipment (Test Access Matrix System), if the fault
IS proved to be in the Exchange, it really is a 50-50 on whether it is the LLU's port or the TAMS equipment ??.