So perhaps I should tear into the steering pad/cover & see if the contacts need a good cleaning, huh?.....But isn't getting the cover/pad off a pain in the a$$? :(

I would suggest all of the above before tearing into the steering wheel. Once you start digging with the steering wheel you put yourself at risk of it going off. When there are lots of things that should/can be checked beforehand.

I agree. Try everything else first, then, if needed you can decide whether or not you want to attack the steering wheel cover, because it does involve the airbag and we will need to guide you though the steps to insure your safety.

Makes sense: I'll run 12 V direct to the horn to make sure it works [I'll make sure it has a good ground while I'm at it], then check fuses, then swap relays....