If you seat the rounds all the way to the rear and #2 and onward won't engage, it means that the rounds are not being forced upward into position by the spring. Either they are catching on the side of the mag well or the spring isn't strong enough to force them up.
Let me guess, when you cycle the bolt on the first round, the second round just sits there not touching the bottom of the bolt at all. Then you fiddle with the round a litte bit and it "clicks" into place so that you can feed it?
It is time to dissassemble your Mauser and take apart the bottom metal. Clean the magazine well and check the magazine spring. Reassemble and see if that helps matters. If it doesn't I would replace the spring, and if that doesn't fix the problem I would install a mag block.
A mag block can be made from a piece of wood very easily. Cut the mag follower to the length of your longest round, then cut a block of wood to fill the remainder of the magazine from the rear (so that your rounds are loaded in the forward position). Sand/whittle/cut the sides to match the taper of your mag well and you have a cheap mag block to see if that fixes the problem.
Polishing the feed rails is for when you have actual feeding problems (such as the round not leaving the mag well once engaged by the bolt, or having the wrong angle of feed into the chamber and getting rammed into the C ring). So I wouldn't polish the rails until a last resort. Remember, if the first and second round feed, there is no need to polish the rails.
Machine guns are awesome until you have to carry one.