In the last couple of years I bought two S/W style dovetails and two sets of sliders from different vendors at different times. One slider came with screws whose heads were too big. They don't look obviously wrong, but the heads stuck out a bit too far, and gouged my nice new paint on the door post. The other dovetail (from A&L, I think) had the correct small-head screws. The screw heads should not protrude above the dovetail surface.
One set of sliders was a very good reproduction of the original, but the other was not so well-made, they sort of looked like the mold did not fill completely. Both sets had springs that were too long and stiff, but fortunately my original springs were all OK. The attached photo shows the repro and original springs and sliders.
My car has the built-in dovetail sockets, and fortunately they were all in excellent shape and needed no repairs.