I've never done one.

I used dino on a 5k interval until about 50k, and then switched to synth. I still maintain the 5k interval.

Frankly, I don't want solvents running through my engine, ever, unless it's off the car and getting rebuilt. As a desperate measure, or if there could be bigger issues on a used car with unknown or known bad history--maybe. I just don't see the point.

Function before fashion. '96 Contour SE "Toss the Contour into a corner, and it's as easy to catch as a softball thrown by a preschooler." -Edmunds, 1998