I use a foam car mag wheel cleaner occaisonally.
It may help .
Spray it on on,brush it a bit with a plastic bristle kitchen brush and hose off.
Don't get it on your face when brushing,it stings[Ask me how I know]

Dinosaur.

"Oh Man I only ride 'em.I don't know what makes 'em work". Donald "Oddball" Sutherland

"Don't let the bastards get you down". Kris Kristofferson

"I am only paranoid because everyone is against me". Larry [Frank Burns] Linville