Dear Door Gurus:
I having a failing door threshold/sill. This is mountain country, high elevation, tons and tons of snow. This spot is flooded with direct sunlight so I guess it got cooked.
Because of snow load, waterproofing is a high concern.

Can anyone give me some pointers for the repair? Does the entire system have to replaced? Or can I just buy some specific part to replace/upgrade the plastic part which has bubbled and cracked.

I want to use only highest quality parts, best stuff. Any upgrades would be good. Would prefer not to have to rip out the door jams (to preserve interior finish work), but will try my best to follow any/all wise guidance.

Many thanks!