Hi Ben
I am really sorry for you.
When reacting rapidely, your WD40 treatment plus wiping the oild residue is very fine.
Paint thinner is dangerous because any contact with paint will damage it. Some use lighter fluid instead. Others use NOCH SR24 (a cleaner that is also a smoke liquid.
Sanding: as you know the issue on rail surface is to create thin grooves in which, later, the oily residue and traction tire residue will accumulate and create contact problems.
So my advice is to use "water abrasive" with a grain of 2000 or higher (5000), of course without water. Water is only used with them to polish paint on car bodies

Don't forget to clean with WD40 the INSIDE of coils (the brass guide and the iron core) and all the thin steel wires on signals etc (cotton swab?)

Coils don't rust? Yes but humidity may stay between the winded enameled wire and cause corrostion or other unpleasnt aging. Maybe a small treatment with an hair dryer will help you.

I am not a specialist as you know but on my first layout in my father's cellar we had water damage (40 cm of water) so I know a bit about consequences. Better a very very thin residue of WD40 which will stop corrosion (especially under the track)

Cheers
Jean

Smoke fluid is essentially expensive kerosene. And sanding the surface of the track is definitely to be avoided. I would try Orange Cleaner as a non-petroleum based cleaner and if it does not work move up to the least strong solvent. I use alcohol on felt furniture pads to clean the surface of my c-track. It evaporates and leaves no deposit on the rails.