It's old school but I've had at least one success regaining water repellent finish when other methods failed by spraying on several coats of silicone. I don't know if it made any difference but I took some care to pull the membrane away from the outer shell when I sprayed on the silicone. Two coats, allowed outside to dry (VOCs and it smells like a bus) in between, allowed me to return my lovingly patched 'old dependable' to second line service as work-wear and riding in the truck.

Silicone isn't all that durable. Recoating every year is usually necessary but after two or three years of getting a regular dose it does seem to get saturated and last longer.

Nikwax makes some good DWR finishes. I used one that gets washed in and polished in the dryer. I've used that a bit but it seems inconsistent. Sometimes extra drying time on high seems to activate it. Other times, not. A friend suggested that some inconsistency may have to do with how long it has been sitting on the shelf.