Testing valve seats with kerosene or similar is new to me, many would use a thin coat of a sticky grease on the valve face to ensure it didn't leak when using kerosene or similar to check combustion chamber volume which would suggest it isn't expected to seal perfectly against a liquid that is known to creep.
It has freshly cut seats, refaced valves, has been lapped and passes a vacuum test, you have done everything, I would send it.
Have you checked run out on the crank?
That may be because they don't have springs installed so non adequate pressure to get valve to seat and not leak. Kero test is done with springs installed
Whats interesting about their vac test is that I have no stem seals installed. Although its new guides and interestingly when testing with valve seats with kero i had only a miniscule amount of weeping down the stem and guide. And it pulled right in the middle of the green section even with no stem seals.
Runout on crank is 0.06mm measured with crank resting on two outside bearings and measured on middle journal