That's the "stop can". It is located on the powered ram of your slide mechanism. The purpose of the stop can is to "stop your slide from moving in" when that can reaches the frame. It prevents the slide from "crushing the trailer sidewall" by preventing it from moving in further than it should. It is adjusted to the proper distance on the slide ram, and then when you retract the slide, that can stops further "inward movement" and the gear mechanism starts to ratchet and the slide stops moving inward.
Here's a pretty good video of what it does and how it works:
You want to be extremely careful if you start "just moving the stop can until it looks like where it used to be" or "tightening it by screwing down the stop nut (it may need to be screwed out to the stop nut instead)....
That stop can is the only thing that prevents your 8' wide trailer from becoming a 7' wide trailer if you're not quick enough on the slide button when bringing in the slide......
I'd guess than when the dealership replaced the motor and realigned the ram, they didn't "finish the job completely" and left (overlooked) adjusting and tightening the stop can....