I buy and sell used flatware. I can take a scratched up 30 year old stainless steel fork and make it look brand new. (In case your wondering, I have sold used stainless steel teaspoons for $90 each that I paid 10 cents each for) You can take deep road rash out of crank arms with heavy sand paper followed up with high speed buffing wheels and compound to bring back the finish. If you parts are satin you can put a satin finish back on with 400 to 600 grit wet sand paper if you are careful to rub back and forth in a straight line until the finish has been restored. A big bar of black and a big bar of white polishing compound is only $10 each. Black digs deep, white compound takes out surface scratches and puts a very high gloss shine on steel and aluminum. That is enough compound to polish over 100 bikes or more. Polishing wheels are cheap.