Teak Treatment in the Tropics
Forget varnishes and oils. Consider one of the modern 2-part + 2-part urethane/acrylics. They are close-enough ''visually'' to varnish and can be hand-rubbed and buffed (if you are a fanatic). My present job on a ''teakey'' is now 6 years old (with one major repair). "Honey Teak" or "Smith & Co. 5yr. Clear" are the names of some of these products. Apply three coats of base for long lasting coating. Expensive but amortized over the time they last ... are sure worth it.
Not butt ugly or butt ugly-lite like Cetol.
Oil? you GOT to be kidding... all that nice black brightwork you see on old boats --- thats an oxidized oil finish. If you must use oil, add 25% oil based varnish to it to make it last and give good coverage.
Honey Teak: www.signaturefinish.com