All very interesting. So I just ordered that Plexus a few days ago and now I read this. Oh well. I have xpel on my M3, full hood, doors, roof, front grill and fenders. My M is space gray metalic so I'm not seeing any yellowing but I do have alot of water spots that won't come out. I haven't tried any paint cleaners or sealents but did try the two products from xpel. One is the cleaner and the other the sealent and to be honest, they didn't do shit. In fact the xpel cleaner actually made some permanent swirls in one spot of the plastic on the hood as I was trying to get rid of one of those small yellow spots that developed.
So what should I do? I don't have pics, but you can imagine water marking stains. Anyway, what do you all suggest then?