Like TC, it has been awhile since I had one of these apart. As I recall there is a small oring at the top of the valve stem that makes a seal between the retainer and keepers. It prevents the retainer from acting like a funnel for directing oil down the valve stem.

The umbrella seals were never factory but some people used them when the guides were worn badly. Other aftermarket seals were (are?) available that require machining of the guide for installation.

All that aside, I have never seen a 235 or 216 that smoked solely because of valve seals or lack of them, except for a puff on startup. If too much oil is getting to the head top side because of an overoiling condition,maybe.