I'm quite new to Dutch ovens but I have an old Falkirk 6 in cast iron. Conditioning an old cast iron pot or pan couldn't be easier, just clean it back to bare metal and then wash it and immediately dry it. It then needs a thin coating of lard ot vegetable oil all over before going into a pre heated oven at 170 degrees C for between 60 and 90 minutes (depending on the mass of the pan, more metal takes longer to heat up)
After it's been in long enough turn off the oven and allow the pan to cool in the oven.