In another thread we've been discussing refinishing a Remington plastic finish stock but after reading thoroughly I believe your question deserves a seperate answer. When dealing with any polyurethane finish it has to be treated almost as one would a paint finish on an automobile. The kicker is color.. Yea I know the finish is clear but it's not, really!! Poly finishes have additives some of which are to make it more UV light resistant. These last are usually a metallic of some sort. I've found the 2 most common give the material either a pale blue or a pale green tint.. Looks clear on the wood but it's there.. If the material you are trying to fix and that with which you are trying to fix it with are the same, no problem.. if not?? Well it will cause the fixes to shine like the proverbial diamond in a goats patoot.. I start a scratch repair by very lightly sanding the scratch out with 400 or 600 grit paper. I use wet or dry and use it dry. The wetting agent would hide too much detail.. The patch material I use is a rubbing poly. I bought it at WalMart but brands are irrelavent. Apply the material with your hands and a couple of light coats just on the the damaged areas are all I usually apply.. Let dry very thoroughly and level lightly with steel furr. That is steel wool of 0000 grade.. It feels like cotton balls but will polish the finish. When complete and the surface looks good I lightly wool the entire stock and give it s blending coat.. This helps obviate any color changes.. If you sand thru to the wood matching the stain can become a problem. Take your time and don't worry too much. You can usually just do it over if something doesn't work out..