Posted for Barry Hancock <sportform@cox.net>:

 Citrus cleaners are very effective....but also etch into the finish....stear
clear!  This from a guy who makes his living polishing high dollar warbirds
who about rung my neck when I suggested I was using it to get exhaust stains
off of the T-28 I was flying for his brother...
 
 Once or twice won't have much of an effect, but the cumulative effect is the
perceptible loss of "luster" of the finish....
 
 Cheers,
 
 Barry