What tool is needed to tighten the valve cover on my 1995 Land Rover Discovery?

I have a 95 Land Rover Discovery Series I and its leaking oil because the valve cover is not on tight. We are trying to tighten it up but none of his tools fit correctly. Today I bought a 7 piece Torx Socket Set and this did not work either. He is quite handy, but we dont know the name of the tool needed to tighten this up. Thanks!|||If it is leaking, tightening it won't cure your problem, and if it does, it won't cure it for long. Its not justr a simple tighten it on up kind of thing with those. Not to be rude, but you can't even figure out what to use to remove it, take it to a shop and have it done by someone who is qualified.