My 92's intake manifold is old and stained. Yet take off the "5.0 HO" plate and you can see the silver/steel color is still under there somewhere. I have tried numerous "cleaning" agents and am on my way to an acid such as muriatic. But before i go there i thought it wise to ask for insight from those that may have gone before. Anyone successfully cleaned up all the old stains from the intake without repainting? What did you use?