The toilet room sink faucet in our Sunstar has had an intermittent leak under the counter since we purchased the unit (and probably before). It was on the hot water side.
Tightening the PEX swivel elbow would fix it for a while, but then it would drip again. That was bad, because the drip was into the sink base cabinet, where it might not be discovered for a while.
Before our next outing, I decided to fix it.
Below is what I found. The cone washer (or whatever that is called) got folded over during the initial installation. I tried to replace it with a cone washer from the hardware store, but it was just too big to fit in the nut.
It took me a while to locate the correct part on-line, so when I found it at Ace, I ordered 3 for delivery to my local store (2 for the faucet, and a spare in case I boogered up one of the first 2).
I replaced both swivel Els today, and pressurized the system. So far, no leaks.
Neither the bath sink or faucet (or stove or kitchen sink, or faucet) were sealed to the counter or sink when the coach was made. So, stray water from spray or washing hands or dishes, can leak under the sinks, stove, or faucets, causing long term damage and problems.
I bought a tube of DAP Kwik-Seal today to seal all of them.