No problem with painting the O14 track. Those metal sleepers would have pretty quickly acquired a nice patina of rust as would the rail side. Since I've never seen bright rusty track this was followed with a weak wash of Precision "Underframe Dirt" and a spot of Humbrol Gunmetal around the fishplates to represent oil.
Less successful was an attempt to dab some weathering powders on to give the sleepers a bit of rust texture as well as colour. In my enthusiasm, I tried this before the paint had dried (I also took the photo too early, hence the shiny bits) and the result was more smudge than I wanted. That said, it IS a nice mucky smudge and since it's powder in wet paint, it won't fall off in a hurry !
The rail head was cleaned up with a screwdriver followed by a DOGA track rubber before the rust colour had hardened - it's a real pig to do later and results in giving in to temptation to use emery cloth with the resultant scratching.