Seacock prob

You could bung the hole and remove the pipe just to check there nothing stopping it closing .
I have replace many sea cock in the water and on land and the one thing I never had a problem with it the hull fitting moving , but let's say it did , you end up with a small drip coming in which mean you have to be lifted out, no harm done the worst that can happen is the hull fitting will break at the sea cock , so best to bung it first .
Of cause the safety way it just to get lifted out and do the job on land .
 
Ended up scrapping the whole lot and starting again, Bumma !

Just done the same and gone for plastic valves from Trudesign. BTW found that Screwfix sell a better quality PTFE tape which is thicker and less prone to twisting and generally making a right mess. Its under "gas" but suitable for water and much easier to use. Only seems to come in packs of 10 for £4.49 so some at home and the rest on the boat.

https://www.screwfix.com/p/ptfe-tape-for-gas-12mm-x-5m-10-pack/49448
 
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