Valve stem oil seals are little rubber or neoprene seals in a metal case that fit on the valve stem, and against the valve guide thus preventing oil from being sucked down the guide and either into the intake tract and into the combustion chamber, or into the exhaust and being burnt, producing a smoky exhaust, especially when hitting the throttle after a long overun, like coming down a long steep hill with the throttle shut.
Changing them means taking the head off, and removing the valves.......... not a hellishly hard job, if you know whats what. I've done cars in my drive in the past.....nice weather, lots of tea, plenty of time.......lovely.....
