Bobcat S160 oil in the header tank

Have a customers Bobcat S160 that has oil in the header tank. I have never worked on one of these machines before so unsure if it is in fact engine oil and not hydraulic oil in the tank.

From what I have read common cause is a blown head gasket or cracked/Warped head due to over heating. They did ring me a couple of weeks ago to say it was over heating so went out and blew radiator out which was completely blocked. Is there anything else I should check before ripping the head off?

Engine...

Bobcat S160 oil in the header tank

Bobcat S160 oil in the header tank