I did a whole spiel on RockAuto and their return policy. I found that the way they work is: you pick the part for your vehicle and they ship that part. If it does not fit, it's your problem. Heavy penalties $$ for ship back. That's what I found.
I do like local parts stores because where I go I can take it back, no questions, no charge and I don't have to wait for shipping. In this case, and it was me, hopefully I would have discovered that WC14493/4 did not work, taken them back to FLAPS and then researched. This was a tough one, I agree. I know I would have looked at the "specialty" vendors, if that's what you want to call them, to see if I could figure it out. Which, in the end, I did, because I really like to solve and find parts. Have had to do it many times when in your position. Hope it turns out good before it "brakes" you.