Do a search mate theres been about 5 threads on this in the last few weeks with loads of replies/cures/fixes etc.
If its leaking around a bolthead, some people take out the bolt, gunk loads of sealant round it, wack it back in and torque it to 12n/m, some people wait till cambelt time, and while its 90% stripped and timed anyway just wip the cover off and re-seal the whole carrier.