Also sounds a bit strange to me.
I am no expert by any means but i have seen 500C and 500CMs from the inside and there were no obvious differences. Of course, i think the upper screen frame could be different and they also removed the aux flap flash contact, but the mechanism itself, e.g. where
things are likliest to go wrong, should be practically identical. As i said before, i am no expert, that is only what i suppose, based on what i have seen.
Things i am worried the most about are those moving parts like clutches or springs breaking, but they seem to be the same in the different models.
But there were several revisions in very early 500C models from the late 50s. The most well known difference is the brake for the auxiliary shutter flaps which caused headache and i think that the whole mirror actuating spring mechanism was completely different in the very beginning.
According to my repair technician, the old models are rare and he has virtually only seen the configurations from the 60s on.
My 500C has the brake revision from 1970 (with the larger rubber disk), just before they changed it to the 500CM configuration with the small o-ring.
https://www.photo.net/discuss/threads/early-hasselblad-500c-observations-question.5514256/
The only instances where spares were needed was with the lenses. I had some $$$ repairs in CF lenses. My technician got the whole spare part stock for the V system and prontor shutters from the official austrian Hasselblad Rep plus he also seems to not be that afraid of the 200 Series:
https://fototechnik-mayrhofer.at/leistungen/mittelformatkameras/index.php
With the 500 bodies it was mostly just CLA. Gummed up grease from 1970 can wreak a lot of havoc in 2021