msulliv3,
Welcome to the forum.
Any build of grease or old oil should be removed if for no other reason than to keep the machine clean. Keeps your hands clean and your work too.
I'm not familiar with the Kenmore 21s, but I'd start carefully with sewing machine oil and cotton balls or a clean flannel cloth. Avoid strong chemicals such as those found Simple Green, 409, Go Jo, Gunk or others.
They can damage certain finishes and decals too.
Joe