Leaking Jandy valve

[waterbear]

Thanks for the info! How often does a valve need to be lubricated? I'll
dig through the previous owner's spare parts bag and see if I can identify a
screw for it.

The part you need is a Jandy grey valve grease cap. It is a plastic knob that screws into the hole on the side of the valve. You can get them from most pool supply stores or online. The valves are supposed to be lubricated every 6 months to a year with silicone lube (same stuff you use on o-rings).
Here is the procedure from the jandy valve manual that I have:

1. Turn off all pool/spa equipment.
2. Rotate valve handle so the OFF on the handle is
over the word GREASE on the valve body.
3. Unscrew (counterclockwise) and remove the
black cap of the grease fitting.
4. Fill cap with lubricant (Jandy Lube).
5. Replace cap on fitting and turn in (clockwise)
until all of the lubricant has been forced into the
valve.
6. Use manual operation to move the handle from
side to side to spread the lubricant across the
seal.
7. Reset the valve handle to its original position
and start equipment.
Once a year the valve should be disassembled
and the O-ring and valve body inspected for damage.
Thoroughly lubricate the square seal and the O-ring.
Reassemble the valve.

Hope this helps.