Flat switch. Its hotter near the switch than mid battery.
Its warmer close to where the ceramic and metal meet. Not so much the actual switch. The cart does heat up, and glow. Just not vaping as well as the initial 3 or so loads.
That's not sounding like a loss in the switch (which would warm the switch body from the inside out) but rather from the bond between the ring and the copper strip up the wall. This too is not a good thing but may in fact not degrade further so you might choose to just keep an eye on it for now. However, it's heat where we don't want it rather than in the core where we do.
Some modest heating is to be expected, I was able to measure it in fact, but it's a matter of degrees you see (sorry, you don't get many straight lines around here you know.....).
AFAIK all units are checked for losses here prior to shipment (we discussed how to do that a while back) but that's doesn't take care of situations like this where it degrades later.
Repair probably calls for stripping the tube down and then rebuilding it in the usual two stages (bottom ring/strap assembly installed followed by replacing the socket plate and retaining screws.
Tough call, if it were mine and
stable I'd probably hold off on sending it in if it was otherwise working OK. Minor self heating (like in the battery) is going to be a fact of life at the power levels we're working at, we can afford to loose a little but not a lot IMO.
OF