I've worked on a few PE engines and/or sets for customers. The primary and most recurrent problem is, as others have already pointed out, lead wires to the engine's pilot truck and trailing truck breaking free, as well as the lead wires to passenger car trucks. I've cut out a portion of the original wire, removed the old solder, wire remnants, and glue (every soldered connection is glued and light bulbs in the cars are glued into their sockets) from each point of contact and spliced in new segments of 24AWG Super-flex wire. Once that's done, I think this set is fundamentally a good value for the price.
Dave
Precision Flyer Repairs - over a decade of S-gauge servicing -- maintenance, repairs, and upgrades.
"Repaired to the point that I'd like to keep it."