Mr. B, if you're still around, mine is a M-1895 - the same gun, really - and the only thing you need to know about it is that you CAN clean the barrel from the breech end by the simple expedient of learning how to remove the lever and bolt. Remember, not to ever let the rod hit the rifling, or you can wear out the barrel by rubbing the grit infested rod on the rifling.
Other than that, just LIGHTLY oil the parts that move, and bear against each other.
The Marlin levergun is simple, and if you learn to take it apart and put it back together, you'll be well on your way to becoming a True Rifleman. Every man should know how to "detail strip" and reassemble his rifle. It's a lot easier than most initially think it to be. Try going to www.dogpile.com
and entering the key words "reassemble Marlin M-336" and see if that doesn't get you to some good sites with good instruction - better than I can provide. Those will likely have pictures to help you. I always learn better with pictures.
Hope this helps?