go to the grocery store/hardware store and buy a box of these to clean the frame with:
for first sponge(s) use diluted soapy water (dishwashing liquid). you'll be amazed at the grime that comes off. even things that look like scratches are just caked oil/mud and will come off. for the 2nd sweep just use whetted sponge(s) with water. After that wipe down with a dry rag. Then you can do a waxing for protection extra shine.