Joe,
The stain is from grape jelly spilled while some mom was both comforting a crying child and making clothes for same child. The jelly spilled on the machine and close to but not on the fabric. She could only save one so chose the clothing which was needed the next day. By the time she had time to wipe up the jelly, it had stained the machine permanently. She considered it a badge of honor for helping her clothe her children.
Might not be the real story but a good yarn nonetheless.