I was only ever familiar with the 535B, so I can't tell you about any issues with the original displacement mag from the 535.
I found this brochure from when the 535B was introduced:
which mentions that all the accessories for the 535 are compatible with the 535B (retro-fitability was often a design priority with Arri), however it also notes that a whole new displacement mag was now available, so perhaps there were issues with the original Steadicam mags. You may need to contact Arri or locate an Arri tech who was working back in the early 90s.
As far as maintenance tips, it's pretty much like any film camera:
Keep it clean, avoid or protect it from dusty or corrosive environments, transport it in a good travel case, store it in a cool, dry environment, have it checked by a tech who knows the camera once in a while. Like all modern Arriflex cameras, they're not really user serviceable, so at some point it may need an overhaul, but I suspect there are fewer and fewer techs with the tools and knowledge to work on these cameras now.