Queenie

I recently picked up a second-hand N Gauge Dapol Terrier (ND-100B to be specific) on an auction site. The listing for this claimed it had been tested and operational in both directions. However, upon receiving it and bringing it to a track for testing, it simply will not run. I can tell it does receive power, since the motor makes noise when power from my Kato Standard SX power pack is applied to the track. I don't believe there is an issue with the track either, as it has been cleaned and my other locomotives will run happily along. (Addendum: mid-way through the writing of this post, after trying again with no success to get it to start, it seems to have moved slightly, but only by like, a nanometer. I suspect this may be an issue of stiff gears?) If anyone has any advice on how I can fix this issue, it would be much appreciated. My first instinct would be to take it to a local hobby shop for servicing, but the instructions included with my locomotive do not show how to remove the body shell, and my local hobby shop is unfamiliar with servicing these engines on account of being North American. Thanks