My home has PEX pipes. The PEX pipe runs under the sink and has a fitting that goes directly on the bottom of the faucet. I noticed that the hot connection would leak about 30 mins after a shower. Did some research and eventually found out the expansion tank for the water heater was bad and successfully replaced it. During my research I noticed the water pressure (measured at the water heater) went from the normal (incoming) 60psi to nearly 150psi within 30 minutes of finishing a shower. At the time the pressure reached 140psi, the connection under the sink leaked. It would stop on its own once the pressure came back down.
After replacing the expansion tank - pressure remained at constant 60psi even after the shower.
My question is since the connection leaked only at extremely high pressure, should I "fix" the connection? By fix I would unscrew, visually inspect, put some plumbers tape on the threads and reseat. Or any other suggestions?