Is it one of the newer ones with the cross bolt safety ?? Or an older model. Will make a good carry/brush gun. That hardned gunk is probley milling/greese that was never cleaned from being new. I know you will get her running like it should.
Do you load the Lever-revalation rounds or the round nose. I never shot the Hornadys in the Winneys I had but they did great in the Marlin.