You appear to have Wilcox-Crittenden Seacox through-hull valves. They are excellent valves, but they do benefit from a good greasing now and then. Also check around them, and look for any signs of leakage. If they have been leaking, you need to lap the barrel and bore to remove any scratches etc. Good tasks to add to the stuff you're doing while it's on the hard.
1984 Bristol 31.1
Alameda, California, USA