Oil leak on transfer box

Hi all,

am new to the site as just purchased a month ago a TD5 2001 model.

now my problem is i have an oil leak I think coming from the transfer box just above the rear crossbar, possible cause please, if i cant find it not that bothered as it is only dripping very little, how do i check the oil level in the transfer box???? and also have a groaning/rubbing noise when turning when pulling off only doe it at very low revs when turning??????

cheers for any help in advance