when i first brought my boat home...the wood step needed attention too....went to boat store and found "starbrite" 3 step teak cleaner..
1 bottle was teak cleaner, kinda cleaned out the black stuff in the wood
1 bottle was teak brightner, kinda like a wood bleach
1 bottle was teak oil, to seal and preserve
i did have some rough edges around the wood i did hit it with some 220 on a da and then started the 3 step process
the more elbow grease you use the better it turns out