5EK Cat Back of Block/Head oil leak

Seeing a few pictures would be extremely helpful here.

Where exactly on the back of the head?
There is a cam cover plate back there that can leak, and a large oil drain passage on the back left as well, all the engines newer than the 5EK use a rubber grommet to help seal this but the 5EK block has a larger drain hole cast in it that the rubber grommet cannot be used with so its just up to the spacer plate gasket to seal it.

Being the block was decked, the spacer plate gasket typically wont leak for quite a while, though it is a common issue on them if additional steps aren't taken while doing the head gasket to really seal thing up to prevent a external oil leak.
A spacer plate oil leak while unsightly and annoying is nothing to worry about if its just seeping.

 

It's a very common place to leak on a CAT. I wouldn't worry about it. Mine did it for years before and after both times the head was off.

 

Coolant dripping from between the head bottom and block deck is another common place due to corrosion (or cavitated ferrels) under the water grommets on the jackets is another ugly eyesore common to see.

Luckily neither issue will stop it from running or any major damage. Just sucks seeing it especially after a rebuild with fresh paint.

Sounds like you've already had them cut during your rebuild so you shouldn't see it for many years. They can also be corrected with Belzona (per CAT) but the cutting is better.

 

It's pretty obvious when the paint is fresh. That paint will fade and eventually you won't even notice it anymore.