When your airplane speaks you should listen.  A spot of fuel on the ground is an example of a subtle hint.  Small issues become bigger ones with time unless they are dealt with!  

Initially I bought a pair of spare CAV-110  drains so that I would have one to pop back in when one started to leak.  I always carry a spare in the airplane and I’ve replaced them in the hangar as well as at fuel stops when the tank was low enough the pressure was lessened.  In 2023 dollars these babies are $15.95 plus tax and freight from Vans so I decided to get the CAV-110 O-rings instead and rebuild the two used units I had lying around at a whopping $0.80 cents a piece.  Knowing its possible I can find the viton o-ring myself and save $0.75 an o-ring I decided to splurge and spend the extra $1.50 to buy some time back.  

The units are spring loaded, have an o-ring and a backup c-clip to stop the unit from falling completely apart and draining fuel out a huge hole incase the o-ring disintegrated and the “plunger” fell out the bottom.  I found that if you use some 0.40 safety wire to hold the spring compressed you can then use some 0.20 safety wire to snake under the old o-ring to pull it off without risking damage to its mating surface by using a knife, pliers, etc.  

Steps:  Compress spring with thumb, slide in 0.040 safety wire in cross drilled hole to keep open, gently remove c-clip, use 0.020 safety wire to snake under old o-ring and remove, remove 0.40 safety wire and disassemble unit.  Now take some maroon scotch-brite and clean the mating surfaces from gunk and corrosion.  Slide plunger back in body, insert 0.040 safety wire, slide on new o-ring, slide on c-clip, and remove safety wire.  

Need:

• CAV-110 o-ring (Vans) to rebuild your spare drain
• Loctite 592 to seal new/rebuilt drain unit in wing

Plane letting me know it wants some love.

Small gob of sealant that is causing the leak.

Time to rebuild – Insert safety wire to hold unit open for ease of disassembly.

Snaking 0.020 safety wire in to pop off old o-ring.

CAV-110 viton o-ring is what you want to order from Vans. $0.80 a copy in 2023

Clean mating surface with maroon scotch-brite.

Prior to re-assembly.

A dab of this goes a long way to seal the threads when re-installing in the wing tank.