Revivex is a water repellent made for breathable fabrics. It is not a water proofer.
The fabrics are waterproof on their own, but when wet, they don't breath, and constant wetness also dirties them and the fabric then breaks down more quickly. So they get a water repellent on the surface (hydrophobic, not waterproof), which beads up the water and makes it flow off easily, leaving a dry surface. But the water repellant wears off and you have to re-apply. Imagine it as a bunch of little hairs standing on end on the surface, just like a dry fly floating on water.
Washing a garment in an approved manner stands the hairs back up, and restores some hydrophobic properties. If the hairs are actually worn off, instead of laying down, then an application of revivex puts new hairs on it. It will improve the breathability of the fabric and extend the life.
Nikwax, though, is a Si based waterproofer. It fills holes and makes an impenetrable film-like surface. It will actually waterproof a garment that is not originally waterproof. They are marketed as breathable (because, well, a silicon film technically does breathe), but it's not in the realm of Gore-Tex. So unlike revivex, if you added this to a breathable fabric, the breathability will get worse, not better.
So if the top was originally breathable, I'd probably wash it real good and go with something like a proper application of revivex (heat application and all that jazz). It won't waterproof failed seams and the like, but it will add plenty of water repellancy, and the leaking seams won't be constantly wet so they'll leak less, plus whatever does leak through will evaporate back out more easily.
If it was not breathable, I'd go with a Si based waterproofer. Nikwax is fine. I've used one called Kiwi Camp Dry, it's an aerosol spray. I like the application better, and it's easy to find at ****'s, Walmart, and the like. My fishing hat has multiple coats of the stuff, as well as camp chairs, spot treatments on the tent, boat covers, things like that. Camp chairs are pretty cool. It rains and forms a puddle in the seat area, you just dump it out and it's dry to the touch.
