Headgaskets usually blow where subject to extreme heat and pressure ie. near combustion chamber or coolant passages. Hence you often find coolant in the oil but not other way around - but not impossible. You need to investigate further eg. any recent repairs carried out on engine which could have caused oil to mix with coolant?
M30 engine headgasket commonly blows near cylinder no 6, as mine did.
I paid about $100AUS for Goetze brand gasket set in Australia - ought to be cheaper in Germany.

Bill G Melbourne Australia