1975KZ400D, head gasket leak, any top tips?

Hi all, as title suggests head gaskets is leaking on my kz400d. There is a lot of oil coming out of the head gasket area. I am fine with replacing the gasket but my question is before I start does any one have any tips that would help to ensure success at solving the problem? Eg use of sealant vs no sealant, best gasket to use etc. The engine was rebuilt by PO recently so they obviously didn’t get it right, which makes me think it might not be straightforward.

Many thanks

 

If you have a head gasket with a sticky surface (OEM) don't use any sealant. If not, you can apply a very thin coat of head cover sealant to the outer 1/8" of the head gasket, keeping sealant away from the metal compression rings.
Also, measure the thickness of the oil passage o-ring. Make sure it is thicker than the combined thickness of the head gasket and the depth of the o-ring pocket in the head.