When the one I got issued finally broke, I bought another from the Bay of Fleas, and when that packed up, replaced it again. That final one still lives in my shed.
There was nowt better for identifying loops, and reccy loops. I could discern different types of modem via it … all kind of useful stuff.
I still have the original 301c …. they can prise that from my still warm dead hands if they are desperate.
54-46 was my number