Crankshaft oil seal leaking

I have a GRiSO 1100 that rounded 30 000km yesterday. My GRiSO has been kind to me, but the oil seal in front of the crankshaft keeps leaking. It has been replaced twice within 6000km, and now it's leaking again. How common is this? Any ideas why it starts leaking again after so few km? Not a big problem, but it's annoying to see the oil residue in front of the engine.

Provided the seal is installed correctly it is not going to be the problem. It has to be either the surface the seal is running on or some sort of damage to the timing chest casting. You aren’t using a nitrile seal when it’s being replaced?

I don't know what material the seals are made of, but I ordered an original part when I first replaced it myself. The second time an official Moto Guzzi dealer replaced it, as I was wondering if I did anything wrong since it started to leak again. I will replace it once again, and check extra for any kind of damage. Thanks for the reply!

The seal should be a brown colour.

You are removing the woodruff key from the crank before you install it I assume? Lubricate the nose of the crank as well with some oil and make sure not to drag the lip of the seal over the threads.