Norm,
I painted professionally for about 25 years, 14 of that here in the Flathead. Decks are a pain in the a$$. Laying flat collecting water, snow, sun etc.etc throughout the year eventually wreaks havoc on what ever you lay down. I've used stains both semi and solid, expensive oils from Australia advertised as the "best" ever (and cost like it was) and they all had issues at one point or another. I have not used/worked with the synthetics like trek but have seen some that were twisted and noodly from the constant exposure.
I've come to the conclusion the most cost effective way in the long run is to go with a medium to light colored wood that has some rot resistance, laid down with counter sunk screws that can be easily removed at a later date for easy board replacement and for oil go with something that is petroleum based and thin without pigment or natural oils like linseed oil(boiled or otherwise).
Eventually the pigment, even in semi solid stains builds up after re-coat and begins to flake and the linseed oil creates a food source for mold to grow and that starts working on the wood. In the past I've told customers that even something as cheap as Thompsons Water Seal, if applied every spring after cleaning the decking off will be as good as anything, won't leave a pigment to scrape and brush off and goes on fast like water when rolled and brushed. It might only last a year or two but has no build up and doesn't feed mold and is cheaper per gal. than most. If you don't like it it's easy to switch to something else the following spring since there is no color to it. It takes no time to apply a product like TWS and a 500 sqft. deck could be done in an hour or two with roller and brush.
Dailys Seafin Teak Oil might be an option too since it has the same consistency of the Thompsons' and was developed for the wood and bright work on ocean going boats. I use it on my wood stocked rifles and unpainted exterior wood doors. More expensive I'm sure but might be worth a try as well.
Either way, some options to try.
