do the rocker cover gasket then go and steam clean it all, then if you get athletes foot powder round that area at the bellohousing youll soon see where the oils leaking from(it needs to be dry fully before putting the powder on), if it is the headgasket there tbh id leave it until it needs done as it looks very slight from that not worth disturbing,
it may also be leaking from the cam seal and dripping down but doubt it when rest of heads clean
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