I had a cheapo Fieldsheer (I think) jacket for a few years and it never leaked, well not for a good 90 mins maybe, might have been 50 quid at a show, but an off road tumble ruined it, (ripped on a log) so splashed out on a very dear £350, Richa fully armoured jacket, It has the half zip at the back and I thought that it would marry with half zip on my Richa leather pants (WRONG!) and it leaked down the front of the chest the first time I was out in the rain with it, trouble is, you've bought and paid for it, and you need it, what can you do, the answer is nought, nothing, zero, dont waste your breath etc, I now carry a PVC kitchen apron folded up, and if I get caught out, I stop (always stop early regardles of mates not wanting to etc) and put on the apron under my jacket, that keeps the wet off my clothes and me inside dry, very sweaty on a hot day though......
There never will be a 100% waterproof motorcycle jacket that undoes at the front, the best I ever had was a couple of hours, and that was a horrible dirty old greasy Barber jacket and trousers.
CLEM