Cleaning of rollers?

I use a Dremel tool with a brass wire brush to clean wheels and rollers. You can also use a Q tip dipped in a solvent to wipe the roller (denatured alcohol, lacquer thinner). And yes, this should be a part of your normal maintenance, as should keeping the track clean. Never use steel wool, it'll get into the engine and ruin it.

When I clean the wheels, I put the loco upside down in a cradle, and run it at moderate speed, holding a Scotchbrite pad against the wheels. Then I take a T shirt scrap and wet it with CRC Electromotive and allow the rag to clean the wheels. Works for me!

It sounds like the rear roller has gummed up and is not spinning but dragging on the rail.

Cleaning the pickup rollers is more than wiping the outside, flow some WD40 or other cleaner thru it then blast the inside clean around the pin with some compressed air. THEN put a tiny amount of conductive lube on the pin or leave it dry. Dry collects less grime but wears more, your call.

Also make sure that the part of the roller that holds the pin in place isn't too tight, not allowing the roller to spin. If you use a Dremel to clean it, you can make sure that the roller is free to spin.

One thing I've used that was like a "wonder product" for rollers is DeoxIT D5, I had two locomotives that seemed to have high resistance on the roller shafts, one shot of this and the problem was gone.  I had previously used contact cleaner and solvent to no avail.  It's great for track pins as well.

If you can remove the roller from the bottom without disassembling the truck, just pop it off and give it a soak in some electronics cleaner.  The QD spray from CRC is great for this stuff.  It's great stuff to have handy for electronics cleaning.  I usually just use the cap or a shot glass to soak small parts in.  You can get it at Autozone or even Walmart in the Automotive section.  Nice scent not really strong so you can use it in the house.

I've also used brake cleaner before, but it's a bit more harsh on your skin.