[ychtcptn]

I find the best way to keep teak is to leave it natural, no oil or varnish. Give a good sanding and then clean with a two part and a 3m pad always against the grain, never use a hard bristle brush. Then periodically use the step 2 when you wash down.
If you want the varnished look build up the teak with a good quality varnish 6-7 coats then finish up with a coat of Awl grip varnish, this should last for years.