Once you've removed the housing from the truck, move forks close enough together to hold the housing with the with the slotted nut facing up. The housing should be no more than a couple of inches off of the floor. Loosen the slotted nut so it is flush with the end of the axle shaft. Using a block of wood pound on the axle shaft. If needed use a sledge hammer.
Check with your local Linde dealer for the O rings. T he big one is probably about 18" in diameter.