I built this door 4-1/2 years ago.
It faces due West and has no roof to protect it from sun, rain, etc. It's a brutal environment for a wood door. The door is Sapele veneer on a stave core core. The finish was PPG Cetol Door and Window finish, 2 coats of mahogany and one coat of clear satin.
I see the door several times a year and keep track of the finish. Last year I thought it needed to have the finish refreshed but of course Covid put it on hold like many other things. When I saw the door this year I was sure it needed to be refreshed. This is how it looked a week ago.
You can see how much the finish has faded, and it's dull. But what you don't see is any peeling, cracking or bare spots because there are none. The great thing about Cetol Door and Window finish is that it doesn't do any of those things, rather, it ages by slowing chalking off. IMO this is a beautiful thing; when it needs to be refinished you only need to clean it, scuff sand it, and put on another coat or two of finish. Because the prior finish chalks off the new ones don't build up like varnish which ultimately leads to problems.
Here is how the door looks now after one coat of 50/50 mahogany/satin clear plus a coat of satin clear.
I intended to apply one coat of full strength mahogany but found there wasn't enough to do that so I added some clear satin to it so there would be. So it's a little lighter in color compared to the original but looks much improved over the aged finish. I removed the panels and finished them separately and then reinstalled them after everything was dry. I think it should be good for another 3 or 4 years.
PPG Cetol Door and Window finish is good stuff.
John