I have had a slightly different experience from Fishtales and yourself Captain.
Needed to reproof my Greys wading jacket a couple of years back. used the Nikwax wash to clean then the wash in proofer as Fishtales recommends.
P**h! is all i can say.
Tried it twice and it let in like a sieve.
Third time used the spray on proofer.
Got the girlfriend to wear the jacket, hood up so that I made sure that all was covered appropriately and liberally.
Fab job, water beading of it like a ducks back.
Due for another shot this year so for me it will be the wash and spray.