I would definitely take them off and inspect closely. The balls can corrode as indeed can the pins they swivel on. Ball valves in DZR Brass are relatively inexpensive items - until you get to the larger sizes, 2" and bigger- certainly compared to cone-type seacocks and can sensibly be treated as a service item to be renewed every few years. Those certainly look as if they have been in service a wee while.
Dont forget to inspect the through hulls. I have heard it suggested you should test them by whacking with a mallet. If they have dezincified they wil break. A test to be carried out ashore I think.
Looks like its suffering from a leak from the hose joint above it, and needs cleaning up to see what its condition looks like underneath, apart from anything else.