Morgan Mare, Sorrel - Sears SR or 1976 Release
It's not often that we're unsure of a release, but this girl had us second-guessing ourselves. She came in marked as #5040 from a reputable collector, and does indeed feel like Breyer's old plastic, but her coloring and finish suggest that she is actually the Sears Special Run model from 1990. Nancy Young notes in her book that the two releases are extremely similar, but generally (though not always) she's found the regular run to be more matte finish and more heavily shaded than the SR.
Feel free to continue the debate if you take her home... No matter which release she is, she's a pretty girl with a warm color, darker mane and tail, and four socks over grey hooves.
This girl is Near Mint with just a tiny brown spot on her left girth line. She features muzzle shading and a semi-gloss finish.
Breyer Model #495601 (or #5040?)