1/10. After running (or every hour of use), remove the air filter to clean in sink with soapy water / dry / reoil. Restart engine to burn out excess fuel, Remove glow plug and drop oil into engine there and the card inlet. Turn over engine a couple seconds to lube the inside (prevent rust), and you're done.

The fuel and exhaust leaves an oily residue all over the truck...so you'll have to wipe her down every now and then.