Understand, that while you can get the surface rust off and stop further rust, the metal is still going to have missing blue and at least tiny pits.
Here's the gunsmith way of removing light surface rust without doing further damage to the blue.
Get a good penetrating fluid like Kroil. You can use CLP Breakfree, WD-40, bore solvent, or other such products, but Kroil does best.
Liberally apply the solvent to the rusty areas, then allow to soak at least overnight, or longer.
Get a brass "toothbrush" and make a scraper from brass shim stock or by smashing the mouth shut on a brass cartridge case. Sharpen the edge of the scraper.
Apply more solvent to the rust, then brush the area with the brass brush.
For harder, crusty areas, use the home made scraper to scrape off the rust.
Once you've got as much rust as possible off, clean off the area and apply CLP Breakfree.
The CLP will continue to "work" on the rust, will stop further rust, and will protect the metal.
Using steel wool, metal polishes and other such methods will further degrade and thin the bluing.
Steel wool tends to "bounce" over the hard rust and wear the bluing around it.
This usually leaves a crater-like area of worn blue around the rust spot.
For breakdown, here's links to an online owner's manual, and parts breakdown:
Manual:
http://www.stevespages.com/page7b.htm
Parts breakdown:
http://www.again.net/~steve/page7a.htm
Parts breakdown AND new parts sales:
http://www.e-gunparts.com/
Most parts interchange between the older Marlins and the new, although it's a good idea to include the serial number range when ordering parts.
When disassembling the Marlin, take care to have the lever partially open and the hammer cocked while disassembling or reassembling the receiver halves.
Inside the action on the left side wall is the ejector.
On the front of the ejector "box" is a small silver "screw".
This is actually a slotted rivet.
The purpose of this is for a cleaning aid.
When cleaning the rifle bore, press the ejector down with a punch and turn the silver rivet 1/2 turn.
This will lock the ejector down out of the way of the cleaning rod, and prevent damage to the ejector.
Be sure to release the ejector by turning the rivet back before reassembling the rifle.
