You guys who have been on here recently know I'm re-doing my head gaskets on the Rover. Well, oooops; they sent me the wrong valve seals, so I'm set back another couple days till they arrive. However, of (more) interest, is that when I pulled the valves, I was really pleasantly surprised how clean they were (after 150K miles!) Sure, there was a very slight coating of funk right where the stems meet the valve, in that "elbow." But really NOT bad! The actual valve seat area was carbon free; nothing. I have used Chevron Techron fuel additive; about one big bottle a tank every 3-4 months for a few years. I think I like that stuff. The only possible downside, is that my valve seals (the rubber "grommet-looking" things that guide/seal the valves as they slide up and down,) were pretty tired. The rubber was pretty fatigued and didn't take much to tear-off.
Now, fuel additive is pretty corrosive stuff. (That's why you don't want to OVERuse it.) I wonder if it played at least a small part in the valve seal fatigue. Maybe not. At any rate, I just wanted to pass along my experience. I use about 3/4 cup in the ZX every other month or so. FWIW.

 

the normal shell gas or VP on the track stuff here.

bummer on the time delay of the parts thing. Gotta hate having an open motor awaiting on parts.