So, I ended up going with a zero down (1st payment, actually) $276 a month 4 year lease on a Brilliant Silver 2021 SV40 with Tech and Protection packages. I managed to leverage some equity out of the 2018 SL I'll be turning in*, and used that equity to get the 4 year payments lowered to be the same as the 3 year lease. Now I'll have an extra year to not deal with all this crap. I spent this evening getting the SL ready to turn in*, removing seat covers that didn't want to go on OR come off, and cleaning the car out, then loading in the OEM wheels and tires. I'm sad about all this, although I won't miss the leather upholstery. I may miss the white/grey interior. I'm hoping very much that I won't miss the Bose stereo. Since rain is now forecast for the rest of the week, I don't expect to drive the car again until I go to the dealership on Friday. <sigh>
* Technically, the dealership is buying the car from me, and paying off NMAC.