Has anyone got any advice on preparing the cylinder base gasket for use? I've searched the service sheets and RR and can find no mention. Should I grease it? Use it dry? Smear with threebond 1215? I don't imagine the cylinder base would get over 200C - so I'm tempted to put a smear of the threebond on.
I'm biased maybe , but I always use a smidge of Wellseal
I oil one side and Hylomar the other.
Wellseal. Degrease both surfaces first with cellulose thinners and stick with the original thin brown paper gasket material.
Additional check - that the two halves of the crankcase are perfectly aligned by feeling for any slight step at the joint between the crankcase halves. The fact that the two crankcase halves are a clearance fit together means it is possible they can rotate slightly, relative to each other, around the crankcase joint hollow dowel.
Any step between the two halves at the cylinder base joint means leaks are more likely.