I own the C&EI RS-1 and GP35 3-rail diesel engines, the engines are highly detailed and run well but applying grease to the truck gearboxes is a major project. The shell must be removed, then the screws connecting the power lead wires to the truck pickup rollers and neutral wire to the truck frame have to be removed before the truck can be removed. Due to the wire routing and access to the two screw heads removal is a very timely process using a lite magnifying lamp I generally have to solder failed wire connections which required further disassembly. Also the owner instructions that I have have no information on the process for removing the trucks to grease the gear boxes I learned the process by removing the RS-1 shell. Reassembly after the truck is greased and installed requires applying the shell, make sure that no wires are pinched between the shell and engine frame. These engines have substantial wire routings under this shell.
I also have older versions on MTH, Weaver and Williams diesels, very easy to grease, the shell is removed then remove the screws that attaches the power lead to the pickup roller, the neutral lead to the truck frame and finally remove the truck mounting screw to the pinion motor and the truck is removed. The motor mounted pinion gear and axle helical gear is exposed for greasing.
Note, my comments should not be considered a criticism of the Atlas O diesel engines, at least they have parts diagrams available for their engines , I have purchased parts using these diagrams from Atlas O and they have helped with technical assistance. My comments concerning the greasing of the Atlas O and competitor diesel engines is only informational not judgmental.