Good tip -most rotor failures are in either the this first two or three inches of the wire or the soldered joint at the slip ring
If you can work out how to press off the slip ring it is just a case of unwinding a turn of wire, replacing the slip ring and re soldering the wire, and often just re soldering the wire will do.
You can check for continuity on the remainder of the windings with the Fluke and a couple of box cutters to cut through the lacquer on the wire
If you have to buy epoxy for the job most electronic supply houses have a potting compound, although I dont know if it is any different to normal epoxy.
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST