Review on ACDelco RC98 15 P.S.I. Radiator Surge Tank Cap - GM Original Equipment by Ryan Barton

There was a coolant reservoir that kept dripping. I took a chance and replaced the lid, it wasn't even the old lid. I suspect the o-ring was leaking. So there is no coolant leak or seal failure on my LQ4, which is nice. FYI if it's confusing why it's being caused by a leaking radiator cap. Note that the boiling point of water (212F at normal pressure) increases with pressure. Relieve the pressure and you can slowly boil off the water in the cooling system, it can be very slow to never notice.