Remove the valve core entirely.
Inject sealant
Replace valve core
Valve at 6 should be fine.
How can you remove it partially? :P
I could imagine you partially removing it - loosening the valve core and then trying to inject sealant. Am just trying to second guess ways you could make this even more complicated.
@hippy started
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Remove the valve core entirely.
Inject sealant
Replace valve core
Valve at 6 should be fine.