As for repairs, and maintenance, I learned the hard way, and have a large spare parts box as a result of the learning experience. I'm not aware of any printed matter on the subject of repairs. Replacement motors can usually be purchased at, or ordered through your local hobby shop. Northwest Shortline ( NWSL ) has can motors in a bunch of different sizes. I've also used a few Kato motors. There have been articles in Model Railroader, and Railroad Model Craftsman, on motor replacements / upgrades / installation in scratchbuilds. The "magazine index" on the Model Railroader site, might give you issue dates, and article titles.