oil leakage 6748 - left frontwheel

[sknudsonlineno]

I have got an oil leakage in the center of the left frontwheel. It looks like it comes on the backside of the wheel, between the wheel and the axlehousing. Anyone who knows if its a seal, which one, and how much work it is to fix it? Will an oil additive in the reductiongear fix it? I guess there was about 2 dl on the floor after the tractor has not been used for 3-4 days.