First thing I'd try is soak all the sections in water with detergent for a couple of days, toothbrush it thoroughly, and then rinse with clean water.
If that doesn't work, Spray with isopropyl alcohol from the drugstore and let it set a while, Toothbrush it off, and then rinse with water. I would test this method on one piece of track first to make sure it doesn't affect the plastic adversely.
One thing everyone forgets is the rail joiners. I would plan on replacing them, you'll never get them clean up inside and you'll never have good contact. And don't forget to really clean the Underside of the rail where the joiners go.
If that doesn't work, Spray with isopropyl alcohol from the drugstore and let it set a while, Toothbrush it off, and then rinse with water. I would test this method on one piece of track first to make sure it doesn't affect the plastic adversely.
One thing everyone forgets is the rail joiners. I would plan on replacing them, you'll never get them clean up inside and you'll never have good contact. And don't forget to really clean the Underside of the rail where the joiners go.