Okay, this is as much an ethical question as a technical one, so here goes:
For woodworking, I use MicroMesh, which is an abrasive used to remove very fine scratches from a surface and create a smooth, glossy sheen. It was invented to remove scratches from airplane windows.
The question - if you had a mask that had a lexan window, and there were light surface scratches (not deep gouges, nothing will fix those AFAIK), would you consider using something like Micormesh to remove them, or would you insist on replacing the window? (For sake of argument, the window has been used for, say, three months, and has a date stamp within the last 15 months.)
Would you repair, or replace? If it was not your own mask, repair or replace?
My gut feeling - if it's not mine, then I would insist on replacement. But I'm not sure I would be correct in doing so, just extra cautious.