N/s rear door seal on 2017 B class

[Luckyphil58]

Hi. I have a 2017 B class sports . I found about a year ago a couple of heavy marks in the rubber at the top of the door. My car was recently in at Mercedes for a “ software update” and I purchased the rubber but looks quite an in depth job as it goes into where the window is seated too. Anyone had any experience with this? I think Mercedes want £140 ish to fit it but I’m willing to try but don’t want to mess it up then it costs me more money to fix

thanks in advance