Going to presume you are talking about a 2.2 petrol .... If it is, they tend to leak (every one I've seen recently) on the front camshaft bridges just under the front of the rocker cover! Easy fix if it's not the camshaft seals themselves! Basicly if you take of the front belt cover (big black plastic bit, tons easier to remove with the alternator belt removed) you will most likely find that the oil is leaking at the very top around the camshaft seals!
If this is the case, to resolve the issue is fairly straight forward. Refit a new gasket, seal around the very front and very rear cam bridges with something like
Loctite 5910 taking care not to block any oilways! Re-fit your top cover with the new gasket installed ... Bob's you aunty It
SHOULD stop leaking!
Main symptom of a leak from here is a misting of oil appearing on the underbody plastic panel that sits below the radiator, usually around the bottom pulley area! All of the timing belt area may also have oil present underneath the cover .... It does seem to get everywhere

Hope this helps you
Graham