alright man I actually have to be an expert on m42 oil pans (since ive broken more then 3 sets of top and lower pans). The lower pan is a snap just take off. Wrench off the 16 bolts or so around it, of course after draining the oil. Then simply lower the pan from the upper pan section. Replace with new gasket and pan. Done!
The upper however is a bitch, especially if its your first time. You have to removed the lower, dipstick, oil pick-up tube. Then you have to Wrench off the 25 or so bolts holding that pan. Then unsnap the mount bolts, and raise the enigine. Once the engine is raised the best trick is to slide a big socket in between the bolt and mount location so you can remove the jack. Then slide the pan off.
Good luck!
-James