In our kitchen, we have installed a water purification system because the water in our area is of very poor quality. The drinking water is delivered by a separate small faucet which sits on top of the sink. The faucet has a detachable arm which is sealed by an elastic O-ring. The O-ring degraded with time and the faucet leaked water. The O-ring had to be replaced but it wasn't easy to find the correct dimension nearby.
I asked a plumber and he suggested to temporarily seal the leak using some Loctite pipe sealing thread. I can tell you now that the temporary solution became a permanent one! The faucet stopped leaking and now it is very easy to replace the thread if needed. The thread package I bought is sufficient to seal the faucets of an entire building!