Hipshot-
Try softening the stains and scum by applying a generous amount of warm water to the grips. I usually do this by really wetting an old terry cloth towel with warm, NOT HOT water and then wrapping the towel around the foregrips. You might have to dip the towel several times. Better yet, is to pour additional warm water on the towel while it is still wrapped around the rod.
After at least 10 minutes, remove the water soaked towel and replace with a clean dry towel or several layers of paper towels and soak that with hydrogen peroxide (right out of the bottle!). Make sure to use the peroxide that is for antiseptic purposes not the type they sell for bleaching hair.
Leave the wet peroxide towel on until the stains are gone and the scum is removable by rubbing with a clean damp towel. When finished, rinse with clear water and dry.
Do not use any type of solvents or products with petroleum distillates since you might ruin the rod finish, grips or wraps!
Hope this helps!
Mad Mahi
TSLTW