Good pictures, Ted; put the Loctite where you have the Yellow Arrow. Grossman will have handrails, but they will be listed under the electric train parts for the 994 (part #339, $4.50). Cleaning the motor is a bit of a challenge... cotton swabs are helpful, but they do tend to leave fibers behind. I usually do my best with WD-40 and compressed air, then use an old mechanic's rag to wipe down what I can, and blow it out with compressed air again. The grime on the gears isn't super critical, so don't worry if you can't get them squeaky clean (Edit - except where you need to put the Loctite, the cleaner the better). I would concentrate more on the bearing areas, anywhere a shaft spins in a hole.
Gary is correct about the spring needing to be wound up all the way for good power. With the square key, you should be able to wind the motor between 14-16 half-turns. When you get past 12, just go carefully; you will feel it when you hit spring bind. It is ok to carefully wind the spring all the way until it binds, but just don't wind it any further. I usually like to count the number of turns when I wind any of mine so that I approach spring bind very carefully, or stop winding just short of spring bind.
Marx liked to tout their trains as having a "Strong spring motor that cannot be overwound". That was true enough for a brand new motor with a child winding it; but on a nearly 70 year old motor with an adult twisting the key, the mainspring or die-cast hub can break. Just be careful about winding all the way to spring bind, and it will be OK.
I do remember having to have my parents wind up my Marx train when I was young (4 or 5 years old)... I just didn't have the strength to wind it all the way up! I got better at it as I got a little older... 
