Hi John.
My next job is to fit the copper rocker gaskets, and gasket sealer is recommended, the manufacturer suggest,s Permatex Ultra Grey 3294 or Copper Coat. Wait 10 minutes for sealant to cure, then tighten down, but wait further 24 hours to fully cure before starting the engine.
I have found similar sealant here in the UK : LOW MODULUS SILICONE SEALANT NEUTRAL CURE again off Ebay, you have to be careful with silicone and aluminium, so standard frame type sealant not suitable.