Is there a gasket behind the timing Belt?

YES, it is called the camshaft SEAL, you have to remove the camshaft sprocket, and you will need to pry the seal out gently, a new one costs $8.00 ( may come as part of a kit from fram you will only need the camshaft seal) lube the inside and outside of new seal with fresh clean motor oil ( weight does not matter ) DON'T USE SILICONE RTV !!!!!!!!!!!!!!, then use a seal installer or pvc plastic pipe as a seal installer and gently tap the new seal into place and you are done!