The model 27 was the flagship of S&W's line until they discontinued it in 1994, and a higher price bought among other things, more attention to the trigger pull. As for your other model 57's, it would take an experienced smith about 20 minutes each to get rid of the gritty feel. Should you send the first one back to the factory have them tend to that.
The sear could be rusted on the other one, but it might also be a brown stain left by the heat treating process, and if so it's harmless.
Not popping the sideplates is a good idea. More revolvers have been ruined then fixed by owners who didn't understand how to do it, and more important - how not to. Do take off the stocks, cock the hammer, and spray some CLP into the back and down the hammer shot. This should improve things, and you won't get into any trouble.