You can send it via JB if you'd prefer. It doesn't make too much difference.

Given you're seeing the issue at least once a day by all indications I'd still be inclined to put a factory image on it for re-testing, and once we've tested it to re-confirm the issue, if it's still exhibiting on a clean factory image, and provided no evidence of liquid/damage (even if you weren't aware of it) - mainboard replacement would be the next step. Graphics chip on those are part of the board.

If you do send it via JB they'll automatically include a copy of the POP anyway which may save you a step if you don't have a copy handy.