In every old Buck I've ever had, and come to think of it, every brass bolstered knife the main issue is verdigris. That green stuff that always seems to form around the snaps and bolsters. Especially in damp weather, once it starts it never fully goes away.
Oil tanned leather also seems to exacerbate the issue.
I've tried all kinds of brass treatments, coatings, and maintenance but they all have failed. The best advice I can give is to go with the color you like best and always remove the knife at the end of the day and wipe it down real good, and look for green deposits around the snap. Then set them apart till the next carry day.
Horror story of mine, I had an older brass handled balisong that I had forgotten about in its sheath. This knife had layered brass handles. When I remembered it and went to check it I had a green mass with a little brass color peeking through and the layers were bulging from the formations inside them. I still have not gotten it all out. Brass and leather do not get along with each other. Especially down here in the humid zone.