Being the new owner of an old 84 323 I'm wondering what would constitute an adequate service for this beast as I'm loath to be paying someone else to do it. I understand the gearbox and diff are sealed so what exactly does that leave?

oil, filters (air, fuel, oil) & anti-freeze in the radiator

thats all i do, ever

Spark plugs. I replace them regularly. I don't know that it does much, but I do it anyway.