I have seen a few lower graded ones with varnish or shellac, maybe the Marlin era ones used lacquer. On pre-13 guns, shellac or varnish was used on most and in a 1906 catalog it gives reference to a Pigeon Grade as "They are all finished in oil", Grade 3 doesn't give reference to oil but states "We are always careful to give as rich a color and as fine a figure as possible ". The A-3 and later the Deluxe in 1913 stated "as many coats as possible to bring out the figure".
Also in ordering a gun you could ask for the finish you liked on any grade as a small option.
