I have a relatively small number of frames and a large number of barrels. Each frame has a list of barrels designated to it's use. Some few barrels are on more than one list but not many. When I obtain a new barrel I decide which frame it is listed for. It's not the only criteria, but how the barrel locks up with that particular frame is most primary in this decision. When you think about how a Contender is made and how it functions, it makes sense that a particular barrel would "fit" one frame a little better than another, and it may not be the frame that said barrel came with. With all that said I don't think I have any barrel that would not at least function on any frame, but some have that "bank vault feel" and some don't. BTW ss or blue seldon enter the equation w/ me.
Now to your point in particular. I'm w/ Keith here. Get rid of the WD-40 quick, inspect and "polish". I give mating suffaces a rub down with 0000 industrial grade steel wool(it won't remove any desirable metal or blueing, but will address rough spots), apply a coat of Brownell's trigger job in a jar and check for fit/function. If more is needed then it's time to be a LITTLE more aggressive. From the sound of your case, I would also remove, clean and inspect the firing pin bushing(it is not difficult),firing pin, and spring. Good luck!
Walt