Mark---
You might want to consider not doing ANY oiling to your real teak. Contrary to some peoples' belief, teak has plenty of natural oil--- it doesn't need any more from you, even after 30-plus years. What the oil that you put on will do, however, is attract and hold dirt. This will hasten the deterioration of the surface wood cells and the dirty oil finish makes a great cutting compound when you walk on the wood, which wears away wood cells.
The absolute best thing you can do for an exterior teak deck is simply keep it clean using soap and water (salt water if your boat has a cored deck). And when you wash the deck, particularly if you use a soft brush or scrub pad (used LIGHTLY), always brush across the grain, never with it unless deck hardware forces you to do this in places. We use a basic string mop on our deck.
The upside is that your wood decking will last a long, long time. The downside (at least to some people) is that you have to be wiling to live with a silver-gray deck. So if you treat your natural teak deck correctly, it will not remain the same color as your plastic planking up above.
And do NOT use teak restorers or cleaners on your teak planking. These work exactly the same as sandpaper--- they remove the upper layers of gray wood cells, exposing the brown cells below, which when exposed to the weather then turn gray. So the owner uses the teak restorer again and more wood cells disappear. The only difference between teak restorers and cleaners and sandpaper is that sandpaper removes wood mechanically where the teak restorers remove it chemically.
-- Edited by Marin at 01:20, 2008-01-08