[willy]

I used Amazon Golden Teak Oil I got from Boaters World. Recommended by a friend. I did not want a outer layer, shell kind of finish.
I sanded lightly and then started applying with a saturated rag. Sucked the stuff up big time. I don't believe mine were ever done since installed.
I applied repeated coats until it would not absorb any more, it dried to a smooth natural wood finish and water kind of rolls off of it. It will keep the wood strong for a long time. I plan on doing a quick coat every year.
Some guys apply stuff that mostly sits on the outside layers as a sealer coat. That may be better I don't know for sure. But I like the wood tone and easy touch up if needed and no scratching. And I know well oiled teak will last a very long time.