Mark;

The stock arrangement for valve seals on a B18 is the umbrella style at the very top of the spring and retainer. B20s had more effective seals at the top of guide. You can easily see the seals for cylinder one if you remove the oil filler cap and look in the hole. Also, heavy smoke during and immediately after high manifold vacuum of engine braking (when getting back on the throttle) pretty much confirms oil is getting sucked past guides.

Cheers