The CEL hasn’t come back so far.
I was planning on changing the oil over the weekend, and decided to put some seafoam in the crankcase. It’s advice I got from a friend way back, and follow about once every other year. Anyway, I accidentally grabbed a bottle of fuel system cleaner, which has the same unique can shape, and added that instead. It immediately thinned the oil and flooded the engine, keeping it from starting.
So I went ahead and changed the oil and filter with generic 5W-30 stuff, and am going to do it again next weekend just to be sure all of the silly fuel system cleaner is washed out.
I also replaced the MTF with Valvoline GM Synchromesh.