You could try the cooling system leak down test, but I'm not sure it will give a very definitive result, given you have a small leak.
Thank you. Did that last weekend. Should done it long time ago (I was loosing coolant for the last two seasons, not much so i did not bother). Found 3 small leaks due to bad hose clamps. Replaced clamps to high quality marine from defender - on last test cooling system was holding exactly 30psi for over 20 min until I stopped the madness. kind of proud of this achievement

If anybody reading this wants to do the same test (highly effective at finding small leaks which you can see only under higher pressure, I ordered kit from Princess Auto in Canada:
Cooling System Pressure Tester | Princess Auto
also found lots of less expensive kits on Amazon but would cost to much to order to Canada.
Wondering if you noticed a drop in the coolant level right after you changed the pump?
I was loosing coolant for a while but I saw traces of it on drip cloth under the engine so did not think it's going in oil.
Trying a new pump would be easier than pulling the head?
Engine was overheating last season even after I replaced thermostat (tested in hot water - worked fine) and flushed coolant and did everything else I could think off. Replacing the pump resolved the heating problem.
If it starts well & no white smoke at start up & it doesn't heat up, the head gasket may be OK.
Starts right away even cold, no visible smoke at all, just water out, and I resolved overheating by replacing coolant pump (but I changed oil before that was done).
Maybe try the easy things first? The tests Mark mentioned would also be easier than pulling the head?
I did cooling system leak down test and found several leaks because of hose clumps, now system holds exactly 30psi for a very long time. but i'm not sure if it helped with coolant in oil - coolant could not get into oil because of leaking hoses, right?
Here is what I would do if it were my engine : Check the coolant for exhaust gas. Examine the coolant for oil. If negative, change the oil, run it for a while, and take another sample. My logic is this : a head gasket separates the combustion chamber from the oil and coolant passageways. The pressures are about 300 PSI, 50, and 15, respectively. That means the most likely result of head gasket failure is combustion gas in the coolant, followed by gas in the oil (probably wouldn't cause any issues), followed by oil in the coolant, and, lowest probability, coolant in the oil. It would be rare (but not impossible) to have coolant in the oil, with a head gasket failure, without the other problems at the same time.
Sounds like a good plan, thank you
So then let's consider a failed exhaust manifold. If this is the problem, you should be able to see coolant inside the cylinders with the injectors removed.
Also inside the exhaust manifold with the exhaust disconnected. Is that the engine with the little O rings on the oil line connecting block to head? A head gasket does more than just compression. If manifold cap end gasket is weeping, over time there would be water in the cylinder and then the pan, but starting would likely show some stuttering, knocking, white exhaust or just plain kluncking. Unless this is bad ,more frequent oil and filter change until you get around to pulling the head.Sometimes running without rad cap tight eases the pressure situation Pulling the mixing elbow for a long observation might help.
I'll try to disassemble it next weekend to see. I was hopping no leaks in cooling system shows manifold is still holding as any holes due to rust would cause system to loose pressure? Or it's not the case?
And thank you all for your help with this.