The models (U23B, U23C, U30B, U30C, U33B, U33C, U36B, U36C) all came out at the same time, and as such I'm going to assume that they all feature the same basic chassis/mechanism. So, to save myself a bit of time (not to mention money), I'm going to review the whole lot of them here based on the couple that I've actually purchased.
Much like the rest of the mid-1980s crop of Samhongsa brass locomotives, these are great looking models and not bad runners at all (at least relative to the era in which they were produced). Pickup is great, slow speed creep is fine, and overall throttle response is excellent. No problems on narrow radius curves. They do run a bit louder than more modern models, but not horribly so. All the gears are metal and the gear towers are of the "swiveling" ilk, so I'm assuming therein lies the source of the noise.
These models have no traction tires, lighting or window inserts. They don't come with couplers either, although MT-friendly pockets (and screws) are provided. The motor is an open-framed 5-pole job. Four wheels per truck provide pickup (via wheel-top wipers). Wires transfer current from said wipers to the motor (two wires per truck). The multi-piece driveshafts are plastic. All axles are geared.
OK, no, not "state of the art" by any means. But still, definitely solid models both in terms of looks and performance.
To remove the shell, unscrew the two screws on either side of the rear truck as well as the two screws just forward of the fuel tank. The shell should slide up and off quite easily at that point.