Cracked head

I changed the Head Gasket on me 109 recently cos there was 'mayo' under the filler cap and on the dipstick. The engine performance improved a lot & all was well. That was about a month ago and all has been fine with the engine up till yesterday until I took the filler off and there is mayo again, checked the dipstick and it's there too..& the engine is getting more sluggish again.
I know the other cause for water in the engine is a cracked head..can this also be caused by a cracked engine block? Is there any way I can find out if it's one or the other?

The weird thing is it doesn't appear to be losing any water.

furst orf did you give yer injun a good clean out to get rid of all the old mayo?
second orf are your breathers all clean and unblocked.?
thurd orf about the only way to check fer cracks is to take yer head back orf and use a crack detector dye.

Also check the following
1. are you losing water ?
2. when running does the rad water bubble? (getting pressurized from a leak)
3. does the exhaust steam for a long time (not just when started)
and as Slob says did you clean out all the old Mayo last time?

I changed the oil a couple of times and got all the mayo out.
I cleaned the rocker cover breather when I changed the HG but I haven't cleaned it since. Is there another engine breather?
It don't appear to be losing water & it ain't bubbling.

Exhaust only steams on start up.

Are you making lots of short journies? That causes mayo to build up under the filler cap.

This last week has been mainly short journeys with a couple of long ones. I know that it builds up under the cap on short journeys but when it's on the dipstick too that means there's a problem?