Martin, coolant emulsified lube oil looks like butterscotch Angel Delight, however if left long enough, it will separate out.............
Here is Kaiser's picture of the cracked block with the liner removed.
I've seen cracked liners on a couple of occasions, and also failed head gaskets, and while certainly much less common than the four cylinder engine, not unheard of and definitely not to be dismissed as never happening ever as a lot of people will have you believe
As you've now got the heads off, drop the sump remove the pistons and liners ad take a look at the block, also it may simply be a matter of resealing the liners, as it's possible for water to track between the liner and block, ending in the sump
Best of luck
Brian
