RE: Scotchguard vs Plastic. I didn't harm any plastic, I didn't intentionally spray any plastic. The "SILVER" plastic on the armrests has a coating that is disolved by the solvent(s) of Scotchguard. Masking would be more prudent than trying to be accurate with the spray.
I started in the rear of the vehicle and had no adverse reaction with any plastic back there. Thus lulled into a false sense of security, I failed to account for the "topcoat" on the armrest plastic.
Fabric protectant was one of the HIGH MARKUP extras (Did you see Fargo? Remember the salsesman pushing sealer?) that the dealer offered. A second coat wouldn't hurt, especially on the armrests, headrests, and console even if you FELL for the huge markup extra that is so easy to replace as a DIY.
Total damage was a minor cosmetic blemish but if I hadn't been somewhat circumspect (I tried to mostly avoid the plastic) I could have messed it up a lot more. I could intentionally spray the plastic of both armrests and wipe off the coating. It isn't a bad appearance without it, just a little brighter silver.
I have turned my attention to other things. LIke having had over 50MPG on my last tank and having nearly 54 MPG on thte current tank. Getting a chuckle at the gas station when a frined helps fil it and thinks there is a malfunction because it won't take any more fuel, shutting off at less than 10gal pumped with a cumulative tank mileage of 506 miles.