The seams are an issue like Axlebrit says. Love the PVA glue idea

The other issue with Goretex/nylon is the pores. When new/clean water droplets are briefly held on the surface and air going by takes them away. Air comes through without restriction. When dirty/old, water droplets stay on the surface and can get through eventually, but together with dirt they stop it breathing and you drown in your own sweat.

Three/Four options:

1. Get a new jacket.
2. Use a fully waterproof rain suit.
3. Throroughly clean the jacket and reproof it.
4. Give up breathable and go for a wax cotton jacket with proper vents/collar/cuffs.

1. is expensive. My last Hein Gericke thing was wet at three years old and cost £200. I pay less per year to insure the bike!
2. Cheap and it works, but you need to stop and put it on/take it off/get at your wallet.
3. Sounds good but I've had results varied from a jacket that worked for a year down to one that dropped to bits at the dry cleaners! All are a total swine to get the armour out and dry. Expect a week and complaints about the rings in the bath if you do it at home
4. Very expensive unless you give up protection. As a sidecarist I have less opportunities to need armour. I can therefore wear a Drizabone horse coat that ticks every box so long as you don't come off at over 20 mph.

Andy