inside the valve springs,if your talking about the engine. if you mean valve stems ,there on each wheel. since your saying " seals " i assume your refuring to the engine head oil seals located on the valve stems inside each valve spring.
If it coats the threads of the plug look for a simple leaky valve cover gasket. Otherwise, (just the electrodes are oily) a valve stem seal is more likely the culprit.
the bead of the tire needs to be broken, the valve stem is fitted from the inside out. take the tire off then cut the vavle stem off from the inside and to put the new one on u got to put the stem tho the inside of the tire and pull tell it pops into place
Valve Stem Seal are designed to make sure no oil will spill into the engine piston as it eat the gas coming from the Fuel injector through the exhaust manifold.
It is a small round rubber are plastic seal with a hole in the center of it, And it goes over the valve stem in the head to keep oil from running down and into the combustion chamber- where the spark plug goes into the head. If you remove the valve cover you will see several springs and they go over the valve stem and seal.
You take the faucet apart and replace the washer and stem seal .
Its wear there is no rubber gromet for the stem and bowl, with a glass-on-glass setup the bowl and stem are 'frosted' and fit together withour a rubber seal
The o ring style seal goes on the lower groove, the valve keeper goes in the top groove.
to prevent the air from the atmosphere flow into potometer
A.Valve Core B.Valve Sealer C.Valve Stem D.Valve Cap
Rubber valve stem seals are the parts used to keep tires from leaking around the valve stems. They provide a tight seal which also keeps them securely in place.
What do you want to know? Take the heads off, remove the valves, and springs to get to the valve stem seals
If the refrigerant has escaped, get a a/c valve stem kit from a autoparts store. They cost a few dollars and come with a stem tool and a few valve stem core that resemble tire valve stem cores. If you still have pressure, you will need a special tool that costs about 40 bucks.