Unfreezing seacock handles

[zoidberg]

I found I could use a small 115mm angle grinder with a metal cutting disc, carefully, to make shallow-angled cuts into the inner circumference of the flange..... then some shallow vertical cuts. It turned out much easier than I'd expected, with no damage at all to the layup. Once I was nearly 'all the way through' a screwdriver and pliers managed to lever the rest away.

I did two that way, in 20 minutes.... and so could you.