I had some dealings with Bulgarian AN12s some years back and they said that their maintenance was nothing like ours with regular 100, 500 and annual checks etc. All they did was consumables and fault repairs between a big strip-down every 3 years or so which iirc happened in Russia.
They operate them like tramp steamers going from job to job wherever the cargo takes them and are often away from base for weeks/months completely self-supported.