[Arran]

If this is one of the rubber cords with a glans where it goes through the chassis, I usually just cut them off, run a new cord through the hole, and knot it on the inside of the hole so it doesn't pull out. It may be an idea to add a washer so the edge of the hole doesn't cut into the knot, but I never bothered. One way to cut down on current leakage via the coupling cap between the B- and the chassis is to use a smaller value capacitor, this takes some experimentation as the set will motorboat and squeal if the cap is too small. It's not something a generally worry about since most AC/DC sets are in wood or plastic cabinets, with wood or plastic knobs, and most have a back.
It's like the repair and restoration books always recommended using an isolation transformer when working on AC/DC sets, I did not have one, so I would normally pull the power cord, except when I was performing an alignment, and not standing on a concrete floor was always a wise precaution. The largest shocks I received were usually from AC radios they had a fault, I had a Victor 118 that had a short between the speaker basket and either the output transformer or the filed coil, if you touched that, and the chassis you would get a nice thump, much worse then the 120 volt line voltage.
Regards
Arran