The way these cameras are designed, dust getting in is sadly inevitable in the field - every time you change a lens, there is no helping it, dust will accumulate. As a result there was a small amount of dust inside already when I opened it despite taking very good care of it and regularly cleaning the sensor.

Indeed, the camera is made in a "sandwich" architecture, where the shutter is layered onto the sensor, which is layered onto the IBIS unit, itself layered onto the motherboard.

Since the sensor has to move substantially to stabilize, and that the shutter is connected to the motherboard without any sealing at all, there is more than enough clearance for dust to get into the motherboard, and it will inevitably happen.

Because of that I expect the guts to be very dust resistant (otherwise we'd see them dropping like flies), because there is really no way of protecting against dust ingress through the lens mount.

The electronics itself seemed fairly robust - thick, high quality PCBs. The most sensitive component, the sensor, is encased behind a (removable) glass protective layer. There were no unnecessary cables inside, most electrical connections were done with spring-loaded contacts that would connect to the appropriate PCB.

That being said, the shutter and the IBIS system did look very fragile, like a Japanese puzzle indeed. I wouldn't attempt any repair that required messing with them.