Journaltex, and other railroad journal oils, meet the AAR specification M-963. This specification has a requirement in it that requires the oil to wick through wool packing. Automotive oils, like gear oils, are full of additives that can plug up the waste and prevent lubrication getting to the bearing surface and should not be used.

In a properly packed journal the oil should be added to the front of the box until it touches the button on the end of the axle. If the waste or pads are in usable condition, the box just needs to be maintained with free oil visible in the box. There is no oil seal at the rear box, so boxes do consume oil in use.

AAR 963 journal oil does not have rust and oxidation preventing additives in it. This was a long running argument at the AAR, but is no longer relevant to them. R and O additives will reduce the problem of etching the journal on cars that sit for long periods of time. Journal oil with R and O additives is available and should be used at museums to reduce journal etching.

This is a good discussion of what oil to use in journals:

viewtopic.php?f=1&t=41521&hilit=Journal+oil

I really don't think it's a good idea to have a metal object left rattling around in the waste! if that somehow works loose and gets turns the wrong way, it could do a number on the journal surface.

The "button" on the end of the axle usually has an OD which is the same as the axle is inboard of the journal. If the oil is above that level, it will run out of the back of the box. As Dave said, do the initial box filling so the level is just below the button. Come back later, the oil will have soaked in to the waste and the level will be lower. When we do inspections, we squeeze the waste with a wooden stick and it should give a squishy sound and seep oil. it is not necessary (or prudent) to refill the box all the way to the overflow point at each inspection. With experience and good record keeping, you'll get a sense of how much oil each box consumes and how much to add to keep it good until the next inspection.