1930 & geneg,
Ok, here's the procedure for refurbing old plastic handles:
1) knock down any raised spots and molding seams with a fine flat file.
2) sand the entire plastic surface with 220 grit sandpaper to remove oxidation, scratches, and other blems, but stay clear of any stampings or lettering on the plastic.
3) resand the entire plastic surface with 400 grit wet sandpaper to a smooth frosty finish, but avoid any stampings or lettering on the plastic.
4) polish the entire plastic surface with automotive rubbing compound until the plastic surface begins to take on a shine.
5) polish the entire plastic surface with automotive polish until the plastic takes on a high polish.
6) spray the entire plastic surface with WD40, and take a soft tooth brush to all the crevices and lettering, then wipe it down with a paper towel. This will remove all the excess rubbing compound, polish, and clean out all the crevices, lettering, or stampings. You're done...
note-- this is time consuming, so it's best to save this procedure for your most favorite and highest valued plastic handled tools.