Dr. Watson ... both your 252 and my 248 were produced during the same timeline. And I know the early 248's produced before 1928 had the single reduction humpback style motor. On the 248 Loco, Lionel switched to the "Super Motor" in 1928. Lionel could very well have switched to the super motor on the later 252 models as well. If true, that dates your 252 Loco to 1927 or before.
When I was procuring my 248, I specifically looked for the super motor. It's double reduction gearing enable more pulling power and slower, realistic speeds (it'll still run off the track at full voltage without any cars). See The YouTube Video
of my 248 pulling 7 cars at speed on a 1033 transformer at full throttle (16 V).
If your not a stickler for original parts. I'd look for the Super motor. If you take a precise measurement between the two threaded mounting holes on the motor I can compare that measurement to the mounting holes on my spare 248 motor in my pic above.
I would part with my spare motor except I'm reluctant to do that with someone new to the hobby. The motor needs some work. For one, it needs a new roller plate assembly. I have that reproduction part but it's not installed. Second, it's original wheels suffered from zinc pest. The motor came to me with new reproduction wheels. But the prior owner goofed when he pressed them on. I believe he bent an axle as one set of wheels "wobble" on the track and that binds the gears. Reproduction axles are available. But since I had a another super motor, the one pictured above is in my box of spare parts.