Most durable paint for exposed wooden sash windows

Hi,
We have a Victorian house with mostly original sash windows and some newer double glazed ones. The house faces south and those windows get a real hammering - hot in the summer and very wet in the winter. The sills in particular seem to need constant TLC. They are currently high gloss white, which I thought would provide the most protection. Last time I tried the dulux weathershield paints but again it has failed and not lasted.

Does anybody have experience with any paints which are more durable in extreme weather? I have seen a few posts recommended Benjamin Moore paints, and also some recommending Tikurrila. Anybody got any experience or recommend anything else seriously durable? Would need to be in a white gloss.
Thanks in advance.

Sadolin Superdec has worked well on my gutterboards.
Trouble is often wooden windows are damp to start with and good paints like weathershield just lock it in then it flakes off.

Painted my porch timber with sandtex trade gloss about 11 years ago and still looks new. Its not just the paint it's how well you apply it too.

Traditional lead milk and chalk paints weren't based on alkyds like modern paints and instead of locking in moisture they allow the timber to "breath". When refurbishing old sashes you often find a window or two which haven't been painted for 60 or more years but which are still in reasonable condition, and have a fair amount of paint left on them. Lead paints have been banned for years, however milk and chalk paints are both still available, if somewhat difficult to find. Only downside is that neither gives a gloss finish.

The problem is joinery design more than the paint.

Modern joinery has V grooves at joints, external edges have 3mm radius and the joinery is designed to avoid water trapping.

The paints which will have the longest life before failure at the vulnerable areas are the most flexible paints.

Sadolin superdec is quite decent -its a blended alkyd / acylic formulation which is reasonably flexible.

Dukux weathershield is a retail formulation.

Go to a trade decorating centre and get dulux trade, johnstones aqua water based.

I used to use Teknos 2600 exterior top coat which is very flexible but its really formulated for spray application.

Dont paint with waterbased until temp is over 12deg or it wont cross link.