Expert help needed Allis 180D

[VicS]

Hello all and Merry Christmas-

About 6 years and several hundred tractor hours ago, I cranked my well taken care of 180 in the winter and it added most of its antifreeze to the crankcase. Took it to a local mechanic and he could not duplicate. Took it home and it happened again, this time I added some snake oil advertising nano-technology and it worked until now. Guess there is a small crack somewhere that opens up during cold temps but closes when the engine is warm.

Question-is the leak in the head gasket or head or is it possible it is in the water passages in the block? I can get a reconditioned head but before I do that I'd like to make sure the problem is actually in the head.
Also, how difficult is a head swap out? I've done all the maintenance through the years, but the hardest thing I did was R&R the fuel injection pump( sent it off for a rebuild-which wasn't exactly easy. Tractor has about 3400 hours.

Thanks in advance for any answers.