I've used NikWax for years, first in the bottle and for the past few years as an aerosol spray, and much prefer the latter. The bottle version required dunking your garment in a plastic tub filled with water + Nikwax and was always messy plus I was unsure of how much remained on the garment. Now, I wash my Dariens in the washing machine and while they are still wet, I spray all the surfaces with aerosol Nikwax then wipe off any excess. And it is best done outdoors.
Yeah, the usual "winter task"...
But I always use a designated, GoreTex certified detergent for washing, 40°C/100°F, no/gentle spin, hang the stuff and apply the Spray On thoroughly on the outer Cotura fabric while it's still dripping wet (special care to joints, seams, flaps, front closures)... this gives the best results... you can literally observe how the waterproofing solvent drives the water out the garment...
They also offer a Wash-In waterproofing, but then you have it also on the inner (sweat) liners... feels funny, despite me always wearing long sleeved/legged functional underwear... rather go through above procedure...
Out on the road the stitches get barely damp, even in heavy weathers, and the GoreTex still works perfectly (whilst you'd instantly get that damp & cold sensation with a soaking wet Cotura shell clogging the diaphragm...)
I'm also sold on their Glove Proof, brilliant stuff... I carry like 3 pairs (summer/mesh, light GoreTex, heavy insulated GoreTex)...
I'm also using a dedicated washing detergent for all the transtex underwear...
Those and leather treatments (Daytona GoreTex boots) are from HEY SPORT, German company...
Another nifty item:
Edding 8150 silicone oil marker...
Perfect for all your zippers, boots, jacket, gloves, pannier liners... as well as the neoprene seals of your pannier lids... I even give the visor hinges and seals of my Shoei Neotec II a gentle care with it...