Jim,
Welcome to ECN, mate.
If you are unsure of the electrical integrity of a cable, I'd move to throw a Megger on it, just to make sure the insulation resistance hasn't been compromised.
Having said that, over here, in the late 90's, we started striking PVC cables that were leaking a green, slimey type substance from the ends of the cables.
(This was often found at fittings or at the panel end)
I asked a mate of mine at the time, who worked for Olex cables, he said that this is the result of cables being in elevated temperatures during the day and then cooling at night.
Fact is, the plasticiser (the substance that makes PVC flexible) in the PVC starts to break down with the heating/cooling cycles.
Let's get one thing straight here, this only affects the first lot of NM or TPS cable that was manufactured back in the 60's, PVC manufacturing has evolved exponentially since then.
Just my $0.05 worth
