Coolant leak at head gasket --- why? - options?

1988 Volvo 740 Turbo B23OFT 2.3 liter. The engine has a confirmed leak at the head gasket adjacent to # 1 cylinder on the right/passenger side. The area is very clean and the leak can be seen to originate at the gasket and not at the nearby water pump.

We rebuilt the engine in January of this year. (Cylinder sleeves were needed, the top of the block was milled true, new pistons, head bolts, water pump, and the head was straightened and milled true-IPD parts)

Prior to rebuilding, the engine was well worn and suffered heat damage and had a blown head gasket between # 1& 2. Prior to our rebuild, engine had overheated and Volvo repaired the head for the previous owner.

This is a project car of with my son - we made an extra effort to do all tasks by the book. The engine was assembled in the basement, torque specifications were 100% followed.

This summer we replaced the gray coolant cap with a new Volvo green cap. As the cool Minnesota fall arrived, coolant leaks arrived from various hoses-the leaks were progressive, I tightened one leaky hose clamp and in a few days, another is leaking. The last hose to leak was a small hose at the turbo-it was a high-pressure leak. Earlier leaks were dribbles. I had explained away the leaking hoses, thinking installation of the engine in an unheated Minnesota garage may have resulted in insufficient tightening of the new hose clamps. Operation and performance of the engine has been normal-no temperature problems.

We are ready to disassemble and repair. I am reluctant to repair without knowing the cause of the gasket failure.

It appears we have: a head that is prone to warping or a coolant cap that does not relieve excess pressure.

If the head is warped-this will be its 3rd failure - we will likely replace the head versus attempt further repairs - best sources for a replacement head?

Comments and recommendations?