I had two that were seized - galley and head
I removed both nuts (24mm) and then used a piece of wood between the nut and hammer to tap it loose.
I had to drill a small 2" hole in the bulkhead to gain access to the head seacock (suggested by someone in this thread) to get enough leverage to tap out the seacock.
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I cleaned them out with blue shop rags before proceeding.
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I used Loctite Clover grinding paste lapping compound and Quicksilver 2-4-C marine grease with Teflon. (found on Amazon)
Both work great now.? I did lap them twice each - cleaning between each process.
They should be somewhat stiff when you put them back together.
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I have a couple more Spartan style left to complete - behind the engine (supplying water to the head (toilet) and the V-berth sink drain.
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Tim R
38MKII in refit
Tim Rivard