Sorry if thi has been double posted. I've had my SSI's since '75. Every 2 or 3 years I clean them (off the car) with SOS, followed by a serious treatment with Simichrome. Leaves them nearly chrome-looking. Have won 2 PCA Parade concours (full) and 32 others with these & w/o a gig for them.
Simichrome leaves them easy to maintain with water & Ivory liquid - on the car.
My 2 cents