What I did was soak a white terry rag with acetone & then grab on to the rail with firm pressure . Hold the rag in one spot for about 15 seconds or so & you'll feel the pvc soften a bit, then move the rag along the rail EXTREMELY slow, it burns,or etches the oxidation off. Once you get it going it continues to burn its way down the rail. Worked great for me. I was shown this technique by a friend with a 28 Harris. Took a couple attempts to get it right, if you move too fast, it will white-out the rail & you have to start over. Hope this helps & I take no responsibility if you don't achieve the same results, good luck...finish with a wipedown of Armorall to protect,,,,,,,,,,,,,,,,,BTW, this rail was heavily oxidized & almost white. Although not perfect, it cleaned up pretty nicely.
