I currently run a Tamiya 501x but years ago I ran a XX4 for a season or two.
Now, racing in Australia in very dusty conditions makes maintenace a real pain, but to be honest I found the XX-4, when assembled correctly, could run for months without any maintenance at all
All of the drivetrain bearings are sealed, and therefore fairly well protected from dust at least, and I always found the the upper chassis tunnels sealed very well indeed.
I could comfortably run my car in these conditions for a few months at least without any reduced efficiency in the drivetrain. I felt this was one of the best features of the xx-4.