Your symptom of power loss randomly reminded me of this fact specific to this style of engine. I had identified that on the P47 chassis and other Crusader, Hudson, or RK 4-6-X wheel arrangement series engines. The front pickup roller arm length could touch the square cast in square guide of the front truck assembly. Because the front diecast truck is painted it takes a little while for this short to happen. Also, variations in track can cause the center roller to ride higher up and short. The fix was to install a specific shorter arm length roller (BD-0000013) in that front position.
According to a RK Hudson parts breakdown, the original roller is a BD0000048 (7.9mm DIAM x 10.7mm W / 22.7mm L RIVET TO RIVET) .
The suggested shorter fix version is BD0000013 (7.9mm DIAM x 10.8mm W / 18.2mm L RIVET TO RIVET).
Comparison side by side.
Appears to be an assembly or sourcing mistake and put too long of a front roller pickup arm and it allows the front 4 wheel pilot truck diecast frame to hit the front roller and since the front truck and frame is ground the pickup roller is 3rd rail, a direct short. The fix is a simple replacement shorter pickup roller BD0000013. https://www.mthpartsandsales.com/shop/search
Again, both my personal engines and all engines sold through our shop we change this front roller to a slightly shorter arm variant and eliminate this issue. It affects more than this engine, any of these railking 4-6-2 frames have been coming with the same issue.
To determine if your engine might have this issue: flip the engine upside down with the wheels facing up. Hold the front truck straight in line with the drive wheels pulled back towards the drive wheels where it would naturally trail during running down a straight track. Now push down on the front roller and see that it can hit the back edge of the square pivoting hole of the die cast front truck frame. That's the short problem. Here are pictures from a New Haven 30-1700-1 Crusader that is likely the same basic rolling chassis.
Insulating the bar with tape doesn't last and wears through in a short time. Cutting the front truck bar away isn't a good idea and weakens the structure. Changing the roller is a simple fix. Check your other engines of this same size and wheel type, and in fact, any newer engine for this error. We started buying the rollers in bulk and changing them the instant they arrive in the shop and even retrofitted any previous engine sold.
This affected several of my personal Railking engines and is now a step I check for while lubricating any MTH engine I get.
Examples include the RK P47 Blue Comet or any other road name, the Crusader series any road name, The streamlined Hudsons and so forth. Again, any new RK smaller engine, we began checking for this interference with the front truck since MTH appears to be using a common lower chassis and front truck and is using the same pickup roller.
The BD0000013 shorter roller installed, it is near impossible for the front truck to short to the roller.