Might be a bit late now...
But you can do a wet test: squirt a small amount of oil down each cylinder bore via the spark plug hole, and then perform the compression test.
The oil acts as a temporary seal - this eliminates dodgy piston rings being part of a potential low compression problem (if the readings stay the same with oil the issue is with non-sealing valves/if the readings are higher, the issue lies with the piston rings not sealing.
Like I said, probably a bit late for you, but will hopefully be of value to others.
Mike
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