I got some stains on my stnthetic stock that dosen't seem to come out. I think it's blood. Anyway when I clean it, It seems to take it away but then it reapears when it dries. Is there anything I can use that would like take a layerof the synthetic off to get rid of this stain? It's a protein stain I am allmost sure of. Anyone else had this problem? 3 of my gun stocks has this problem and it is annoying when I look at them.