The 90's sentra has a bad problem, the plastic headlights tend to fog over and yellow severly with age, atleast thats how my headlights were. There are many posts about replacing the whole fixture but I restored mine to brand new condition using Permatex Headlight restoration kit..real cheap about $12 at autozone and it makes the headlights brand new....i just did mine and it worked great so i thought i would share....
Save all the components from that Permatex kit. I too have found that it works very good, but now that you have taken the original, perhaps even coated, surface of the headlight off, the "wear" will return maybe even a little quicker than it took originally. That kit also works good on CDs/DVDs that have been scratched to the point of being unusable. Use only the highest grade paper you can get away with and put alot of elbow grease into the polish and they will play again.
I use Meguires PlastX, same problem, same outcome -- it looks great.
Better than buying OEM lights at the dealer for $400 (crude estimate, but probably not far off).
Plastx is the best thing ever!! I used it on my headlights, and it worked great.
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Minor Modifications To My Car: Razo Shift Knob, Eibach Sportline Springs, KYB AGX Shocks, SS AutoChrome Header, Custom Cat-back, Injen CAI, B&M Short Shifter -- More to come soon!