are available for that valve. If you disassemble it youíll find the handle turns a big rubber plug
with a hole in it that either aligns with the thru-hull to let water
in or goes crosswise to block the water
flow. The T handle is used to compress the rubber plug
to lock it in place. Loosen the T handle before turning the plug.
There are two failure modes that Iím familiar with. If the valve is left closed for a long period of time, the rubber swells into the valve openings and makes it very difficult to open. If you disassemble the valve you may be able to sand down the rubber bumps that prevent it from turning.
The other failure Iíve seen is the shaft disconnects from the rubber. If that happens youíre just screwed.
Take it apart and see what condition that rubber plug is in. Then decide to replace or not.
I donít think Groco has made those in about thirty years.