I've done the soapy water spray trick around the cylinders/heads and carb insulator (which I found was also leaking, but has since been replaced with a new part).

I can't see any bubbles so far but I'm waiting on a flywheel puller and will spray on the left crank seal and do a visual inspection.

Thanks for the tip about using 2 gauges for both cylinders; I'll pick another up tonight. Hopefully I'll have a concrete idea of the scope of repair by the weekend.