could be the bad head. But until it tosses a cel of miss fire. they may not want to dig that deep. Not that this is going to help you. There was post a post where a guy logged the data on fuel and its effect. 87/89/91 The motor is pulling timing on 87. I know ours on 87 can even get into knock. 89 shows a gain of MPG better timing. 91 no gain.
I know i will get flamed on this. I have used it before and even tested it to failur once. In a 20R yota. Ran it with no water until it melted down on a freeway made it 60 miles no water two miles from home . melted at the valve seats and every part that could melt did, all most caught fire. But the block still looked fine the piston walls were fine! we went to a Junk yard and replaced the head and all the wires plastic parts... It ran like a clock for many years after..... Slick 50.
Our 012 runs well and though it has a slight tick its not as bad as others I have heard. it has about 17K on the clock. a slight vib at idle but not much. Just put slick 50 and the thing sounds100% better. i am not amazed as I have used this stuff 30 years. even at cold start it has no sound of needing to pump up.
let the flaming start...