To add to Yngmar and Geoff's comments:-
" Sunsail" and "Whitsunday Rent A Yacht" in the Whitsundays ( Hot Australian Sun) clean the teak on their charter boats once a year, other than the washing down after each charter. They use the 2 part Snappy Teak Nu to clean the decks and then seal with 2 to 3 coats of Semco sealer. Over the last couple of years I have been a part time instructor on one of their boats. I haven't noticed any difference in slipping as a result of this treatment. After using the snappy teak nu to clean the teak, the teak looks brand new. The sealer then changes the whitish colour to a more golden colour. As a result of this, I have done the same to my boat. I haven't noticed any problem with the caulking as yet.
Hot sun does tend to kill teak faster and that is why most owners in Australia shy away from teak decks. Cockpit seats and floor is usually the only teak. Teak is often too hot to stand on compared to white fibreglass.
The sealer does appear to inhibit the fungus growth as it gets into the grain. The trick is to apply a number of coats of sealer. The teak really sucks up the sealer. In my opinion, the sealer appears to harden the teak and reduce wear. I suspect, but can't verify, that the sealer inhibits the growth of the fungus ( Greying) of the teak.
The only way to remove the pitting is to sand the teak, but as Yngmar warns, it is thin and should be avoided if possible.
Many of the boats on display at the Sydney Boat Show each year are owner's vessels that are up to 2 years old. To prepare these to look brand new, they often sand the teak and use " Nappy-San" to clean and whiten. I'm not sure what the European equivalent of " Nappy-San" is and not sure of the active ingredient. I think it may be chlorine based. I would not recommend that this be done too often, but the results look fantastic.
Craig
" Shirley Valentine"
Gold Coast
Australia