Took out the Merkel 500 to give them all a once over and noticed some weird brown stuff on the fore end lever. It is case hardened possible rust? May have been on there since i got it I seem to remember asking about this before. In any case how best to remove it? Rubbed it with some oil looks a bit better. Kinda strange as no other guns exhibit any signs of corrosian. Is this a case hardened deal?