duff S4 coil

****in magic! I work my buns off 5 weeks out of the last 6 looking forward to a shot on my bike, pull the cover off it and the fairies have turned it into a single. Although the plug on the front pot sparked OK when turned over, it wouldn't run below 2000 rpm back in the engine. Put in new plugs, no difference, so I swapped the coils around and the fault migrated with it (you can tell which pot is out by the temp' of the ex' pipe) so it looks like a gubbed coil. A new one is on order but my weekend run is oot the b#stard windae, and once the new one is in how do I know it won't expire in the next lot of bad weather?
Has anyone else had this bother? and if so is it because of (as I suspect) the bloody stupid location of a high voltage ignition coil, right in the path of salt, grit and water with not even a rubber sleeve over it. I was going to totally spit the dummy and blame the Italian electrics until I noticed 'Denso' written on the coil.
Bag o' sh!te man. Wish I still had my Africa twin, at least it worked in the winter.