I agree. I`ve got one in similar shape but keep it oiled. I kind of like the patina on mine. Gives it character...I'd say...
Just Lube and Oil it well, wipe down lightly with Oil, and, leave it be otherwise ( other than to go Plinking now and then ).
Trying to 'clean' it, you will loose what little actual Blue it still has, and make it look 'scrubbed' and or messed-with.