Blown head gasket is one of the  most popularly cited
causes.

You just had the head rebuilt, so that might be related to
same.

A couple of ways to check for blown head gasket - with the car cold -
remove the radiator cap - make sure the coolant is full to the top of
the neck of the radiator - crank her up - if you see the coolant
jumping - you are getting exhaust into the cooling system.  To figure
out which piston is leaking - pull the plugs - the one with the red or
green maybe yellow crap on the end of the plug is the problem plug.

If the engine did not get hot and warp the head - you should be able to
replace the head gasket without problems - observe the head bolt torque
sequence - amounts and so forth.  Bummer to get to the end of a project
and find out it has to be redone - oh well second time is more fun - oh
does that include redoing engines?

IF you do replace the head gasket - when tearing it down - use an eagle
eye to try to find where the gasket failed - carefully check everything
for that location - a burr on the head/block whatrever. good luck

Oil in the coolant is common after a head gasket change. When you find it,
just slurp it out of the rad with a turkey baster.

If you are not experiencing any other symptoms and the oil presence does
not increase, then don't worry about it.

I would just like to say thanks to those who responded to my problem.  As
of now, it appears to be left over oil residue.  I don't know why it took
a couple of months to surface, thanks again.