One thing I don't understand is why manufacturers don't add any drainage or ventilation to lights. It's a well known problem of water intrusion and it doesn't have to be a manufacturing defect but just minor damage.

The easiest fix is an 1/8" drill bit

It's not just lights either. Plenty of vehicles get water pudding in trunks and floors. Just recognize that keeping water out is very difficult, finding a leak even more so. The standing water is the big problem, let it out.

Modern day car ownership outside of the OEM warranty means owning a liability. Even when under warranty- the problem may have no fix and the customer gets strung along for a BS ride. (Think dual clutch Ford transmissions)

A big reason I like older vehicles, all the problems are known and solved.

My 06 Ram sliding back window has leaked for years, I’ve drilled more hole in the channel but done with it. That black gooey stuff they stick under windshields is next sealing the whole sliding part. I looked into a solid glass but was quoted $600 to install.

We did a lot of warranty repairs on those Rams, resealing the back slider-window assemblies.
A lot of the leaks were at the top, and the sealing could also be pretty poor at other areas around the perimeter.
Frequently it was actually the CHMSL above the back glass leaking.
Ft cab lights were another occasional leak source.

I tell so many people that come into the shop that there are 3 things you need to have with any late model vehicle.

A factory warranty that covers as much as possible
Full coverage that covers as much as possible
lastly deeppocket books to cover what the above does not cover.

Are you sure the leak isn't coming from your 3rd brake? It's a well known problem in that era truck.

https://www.detroitmuscletechnologi...asket-chmsl-leak-repair-adhesive-backed/

Think thats bad price one for a Super Duty. Or even better a newer Benz.....

Its a double edged sword. People want all the tech- all the niceties bells and whistles and the MFGRs are happy to give it to them. No one takes the time to consider what the cost of that tech will be 5 plus years down the road. Toyota as a business would die if they built their current vehicles to the quality standard they established in the 1990s. I know why the MFGRs switched to electric blend door motors- but my god it can be thousands to replace them deep in a dash. Cable and vacuum blend door operation is notwancient and maybe barbaric- but it worked fine for the second, third fourth etc owner of that vehicle as it aged.