If the coating has gone it will never be waterproof again. However the various wash in / spray on proofers should make it water repellent again. I have just used some on my kit and am amazed at how well it works. Nowt to lose but the few quid it costs. I used Graingers stuff from Tisos.
Utter bollocks, but you say it with such conviction.
1. As above, eVent and Gore-Tex are both ptfe laminates, the waterproofing comes from the membrane which is durably waterproof - it'll leak if you puncture it, but otherwise will last for a very long time.
2. The coating is something called a DWR - durable water repellent - treatment. It coats the fibres of the face fabric, the bit on the outside and stops it absorbing water. If the DWR wears out, as it will, the face fabric soaks up fluid and gets heavy but also reduces the breathability overall leading to condensation on the inside of the jacket - you get wet, but it's not leaking.
3. eVent as already mentioned, can be washed with normal detergent, needs to be in fact to get the dirt out effectively. I double rinse after washing.
4. Heat treating with an iron (careful, don't iron reflective bits or you'll kill them) or a tumble drier on low (careful, if the thermostat is faulty it can melt bits of trim etc plus tumble drying abrades fabrics - guess what that fluff is in the filter...) may revive the DWR. try splashing some water on the surface to see if it beads and runs off.
5. If you can't do that, you need to reproof the garment, or rather restore the DWR. Grangers and Nikwax both do suitable stuff, the latest new Nikwax version is claimed to last up to five times longer' and seems good. Neither brands need heat-treating except the all-in-one washer and reproofer from Grangers, but it may improve performance slightly.
6. The rattle in my Pikes mixed with excess play and travel was actually a loose circlip, fixed.
7. TJ, I'd stick to your other career as a professional lawyer.
8. I'll say it again, membranes like Gore-Tex and eVent aren't likely to leak unless they have a hole in, seams might if the taping goes, pockets and zips can, depending on construction, water comes through the big hole your head fits through regardless - try a Buff to slow the process.
If the DWR goes, the surface wets out, you will get wet from condensation and it may feel like your jacket is leaking, but it probably isn't.