This has happened to other M3W's but is not "normal" or acceptable. There should be 330 ml of oil in the bevel box, if it is overfilled this can cause leaks. If the input shaft seal needs replacing it can be done in situ, the big retaining nut is a LH thread and you will need to make a gag to hold the flange. Use a Viton seal with a higher temperature rate than the original failed one, size is 55x42x8mm R23 double lip but check dimensions as there are possibly two different sizes used. Mark the nut in relation to the shaft so you can refit to the same position and preload. It all worked well when I did it. Use some silicone sealant on the splines on assembly.

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