My son-in-law bought an older Grady-white boat recently. Most everything is fiberglas but there is a small amount of teak which he power washed. After power washing, there is some teak that is a weathered gray with no finish and some areas that have an old film finish on it. I am assuming the old finish if a marine varnish. What is the first step, sand all the teak? If so, does all of the old finish have to come off even if it is still sticking to the wood? Does he have to sand all the gray off to get to good wood? What kind of finish should he use? He was told to use an oil finish, but I don't know if there is an oil finish that would stand up to the rigors of marine life. Any help would be appreciated. Thanks.

Dick