I recently cleaned a teak swim platform on a Ski Nautique. Not wanting to F... it up, I called West Marine and they gave me their tech support line, best 20 minutes I've had in a while. That guy was an old veteran of boating, the marine version of Grumpy! I took every bit of his advice, do NOT sand it, clean it! West Marine carries this stuff called Te-Ka Teak Cleaner kit, $34.99, go ahead and get a couple 1.5" paint brushes too. Now, get 2 solo cups, need one for Part A and Part B, label them and the paint brushes, wet the teak, apply Part A, wait 5 minutes, apply Part B, then hose off, mine took a second round. Be sure to wear gloves and eye protection!
Let it fully dry, 24-48 hours, add Teak Oil!
Done