Shielding cracking in end-cap tails

As part of scheduled maintenance, we are inspecting and replacing the tails in our inventory of conventional S4 lekos and pars - on occasion, we've had a fixture arc-ing. While we replace with high-temp shielded wire, we still notice that there is still occasional cracks and breaks appearing in the shield. Initially, I thought the culprit was the strain-relief at the end cap being a hard-edge for the wire to be regularly flexing at, but these days I'm not so sure. Has anyone experienced similar issues and has anyone devised a solution beyond regular inspection and replacement as needed?