This has been one heck of a rainy winter! Touching up spots where lots of water has washed the finish off my aging Belstaff Trialmaster is easiest when done with a bar of Otter Wax.
The strap of my camera and overnight bags tend to wear the waterproofing off my jacket. At room temperatures, simply rubbing a bar of Otter Wax over the areas that need a bit of help takes care of it. The wax takes a few hours to cure, but you can wear it immediately.
Nikwax is super easy for a full coat refinish, but as my daughter has remarked, it doesn't look as nice as a new coat of real wax. 10-15 minutes with this bar, after the Nikwax has fully dried, will also fix that. Still far less work than using a creme wax.
I find that most years a single treatment will do, but this year I've put the jacket through a lot of travel, and a lot of rain.
Otter Wax Large Bar, All Natural Water Repellent, 5oz Bar via Amazon