on my 96 contour the lenses lookded dirty, but it was not inside the lenses.. its the plastic on the lense breaking down.... use a magnifer and look at it close you can see the plastic is turning yellow?? if thats what you talking about then take some Turtle Wax Polishing compound, cost about $1.79 a can and open the hood and put some duct tape on the sides and bottom of the lenses to protect the painted plastic/metal fenders and use a damp face cloth and put some compound on it and rub for about 5 to 10 minutes each lense..... wipe it off and look at it under the magnifier again and you will see that some of the stuff is coming off.... it took three polishings to get mine clean.. i also used a polishing bonnet on my electric drill on the lenses and they look like glass not, real clear... i read on this and other sites about using some 1500 and 2000 grit
sandpaper: tried it on a broken piece of lense that i had and found that it took too long as it clouded up the plastic lense and left it all scratched up...... so done use the sandpaper or you will be sorry.....
take the duct tape off when finished and wipe up the adhesive off the painted material with some WD-40.
hope this helps.