I have had such trouble with them that I break my own rule of using sealant where it is not supposed to be used and use a little silicon gasket sealant on the whole of the gasket rather than the eight separate points on the cam caps and tensioner to head surface transition points that MUST have a small amount of sealant applied. I go to great lengths to make sure the cover and head are spotlessly clean to allow the sealant to adhere and even then they still occasionally weep which is very irritating. If they leak after I have done them I recommend a new cam cover and this usually deals with the problem. A leak from the back is often the tensioner/adjuster base gasket but a cam oil seal leak is normally very clear to see with the belt cover off.