This is how I replace the oil seal ring which should keep the flywheel dry of oil. I re-used an old toothbelt gearwheel from GM and adapted it on a lathe to take up the central M18 bolt, taking care of having parallel surfaces which will later press against the oil seal. Pressing the new oil seal into place is a piece of cake now. Take care to rub grease/molykote on it and a few drops of oil. The first revolutions will be without any oil from the crankcase so this first lubrication prevents ruining the seal.