changing valve or head gaskets on 94 b3000

[MUDDING B-3000]

well my engine is leaking oil down the back of the engine i thought it was the tranny but not tranny fluid , and my auto mechanic teacher told me that it would be either valve cover gaskets or a cylinder head gasket and is that hard to change on my truck? and could this be the problem of the leak down the back of the engine?

 

[MUDDING B-3000]

ok sweet ya i check behind the valve cover to see if i could feel oil but i didnt feel anything but i was in a hurry so i might have not felt far enough backto feel the leak. but ya i check and hope its that thanks alot for the advise.