Nothing's going to look good-as-new after 5 years of constant beating sunlight.

I'm a little confused by your timeline, but if I understand you correctly, you built the old house 18 years ago, then moved out. Then 5 years ago you went back to look at it and the deck still looked good.

Do I have that right? If so, I'd say whoever has owned the house in the meantime has been keeping up with the maintenance while you were gone.

As far as recommendations, I'd suggest Ipe Oil. In spite of the name, it's a good product for any type of hardwood decking.

This is a question i would explore locally...depending on where you are calling the tropics....the wood you choose should be researched first...then explore the best product used locally...i would also limit the size of your decks and to areas located for best sun exposure at the time of day they will be used...also plan where deck covers will be needed reduce sun into your home interior...most people plan decks for how they look rather than they will be used...adding vast expansions of deck that are rarely used ..exposed to so much direct sun that they need constant care...many tropical areas have extremely hard woods that will last forever with little care...so look into what the locals use..perhaps post more details here as to location and how you will be using your deck as well..

After trying several of the water-based products over the years and having problems, I am now using PPG Proluxe, but I cannot yet vouch for its longevity. It used to be a Silkens product.