I like it! I'll take a shot at it but Seated quarters aren't my series. With that being said, I like it as an XF45 but if the photo is hiding luster, I could see it as 50-53.
45-53 would be my guess. I too just parted ways with a 76-S in about the same condition. Alas, she now resides with the LostDutchman and will likely be back up for sale soon. Mine had a bit of nice toning going on.
I guess this is the case of "cabinet friction" instead of wear. I was figuring minor wear...55ish with a TPG strong arm for the darker toning to get to 53. Without seeing the coin in hand, and having a good light to see the luster breaks (if they are there), it's hard to see where we may have all missed the MS grade.