My treatment for teak is to scrape off damaged and peeling varnish
, a sharp edged plate or blade held vertical to the wood works well but requires glasses or goggles.
When clean and dry apply a very thin coat of varnish - 10% varnish the rest thinners. This is to soak right into the wood and especially any cracks, crevises and screw holes that might leak water
in deep. Next coat, while still wet ideally, is 30% thinners, repeated until the top face all dries to a smooth sealed finish.
Finally a couple of coats of 10% thinners to put a top dressing on.
This is actually quite quick to do, the scraping is the hard bit but it also prepares the wood face for the wet coat to soak into the surface.
Certainly in my old boat, which was bare cracked wood in many trim places, this approach survived intact for the two years I had her, and showed no degradation.
Those wet coats are the important one, getting a gloss is for show boating