I cleaned up the area around the crack with a degreaser (gunscrubber) and taped it with aluminum (metal) duct tape that I had on hand. This tape is sticky as hell, so get it where you want it before contact is made with the backing removed. It held up pretty well for about 3 months, then I could tell it was again leaking slightly.
I have a bit of positive news to add. I went to the dealer and the new valve cover was ordered on June 6, 2022. I checked for status about every 6 weeks until finally when I called in mid January 2023, the dealer admitted the part had arrived a month earlier but the service guys were unaware. Anyway, I scheduled it for earlier this week and it has now been replaced under my extended warranty. Finally!
I hope this means the dam has broken and the new valve covers will be available to all who need one.