Okay so my gearbox is back in and everything is dry and sweet after a few days of use.
Here are the part numbers for common SAE O-rings that can be had at industrial supply shops:
Camshaft Oring - BS145V (SAE 145 Viton)
$7.75/EA
Bearing housing Oring - BS164N70 (SAE 164 Nitrile 70)
$4.50/EA
Flywheel Oring - BS037N70 (SAE 037 Nitrile 70)
$1.09/EA
Hope this saves at least one of you the hours and hours it took me to avoid shilling out for a seal kit. These are readily available which = less down time. We're supposed to burn the oil, not leak it!