I use plain 5W20 motor oil for rods and axles, works fine and doesn't gum up like a lot of lubricants. I currently use Red-N-Tacky for gears. I personally think it's more important to have any lubricant on things, and the exact type isn't as important.
I actually dropped an ERR Cruise Commander "M" into my A-5's to give them better speed control, really makes a difference in running. It's pretty cool to see the two little guys pulling a string of cars around.