Vinegar will brighten brass.
I take out a bowlful and spread it onto the track with a Scotchbrite pad. I use the hardwood endgrain of a wooden block to rub the track, but I have used fir endgrain as well. Softwood such as pine would work more slowly, masonite would work well. I don’t think the Scotchbrite scratches brass, but if it does it’s very minor as far as I have been able to tell, and in any case the wood block treatment polishes the track back to like new very well.
The main point is that I want my rails to be scratch-free and shiny as new, so I avoid abrasives.
I do this at the beginning of the spring season to help that first train to get moving. Sometimes the Scotchbrite’s not even necessary, and just the woodblock and a little elbow grease seem to be sufficient. The trick is to get that first train over the line, and from then on it’s a cakewalk.
I clean my track about as often as I take a bath: about once every three years whether I need to or not.
I try to run at least one track-powered train over all my mainline track every day. The more I run my trains the less of a problem I have with both oxidation and dirty rail.
Only metal wheels are permitted on my railroad. I have found a good source of metal wheels in odd sizes to replace the stock plastic ones in locomotive leading and trailing trucks. I obtained a variety of Gauge 1 tinplate wheels in various sizes from a local toy train restorer. The flanges are a perfect match.
Coming from small-scale model railroading, I am constantly surprised by being able to turn the throttle and have my large-scale trains actually move in reliable response.
I used abrasives in those smaller scales, before I knew better, and it seemed that when track was new it only needed a little cleaning now and again. Then it seemed to need it more often. Finally it needed cleaning virtually every time I wanted to run a train. This would often cause me to just not bother, and to put off running trains, which I did less and less frequently…
In smaller scales I was never able to operate trains daily as I can now. I have no doubt whatever that daily running is the big secret.
I avoid all abrasives on my track. The pitting and scratching caused by abrasives gives dirt a rough surface to cling to and causes more arcing, which leads to further pitting in the rail surface, and thence to a downward spiral in track quality and an ever-increasing need for track cleaning. I believe this downward spiral was the cause of my troubles in those bad old days. Best not to start down that road.