Our 1997 V90 had several coolant leaks in this area. First, I replaced every hose on the car but the leak did not resolve. Closer inspection found that the water pipe which runs from the front if the head under the exhaust manifold had rusted and become porous. It would weep coolant. I wanted to replace the pipe, but it is NLA from Volvo and no aftermarket option. I removed the heat shield, vacuum pump, and preheat assembly. Not wanting to pull the manifold for fear of breaking studs, I had just enough access to wire brush the water pipe and paint with three coats of POR 15. It appears to have worked.

Our car had a second small leak at the back exhaust side corner where the head mates to the block which would drip onto the transmission bell housing and exhaust header. I assumed an external head gasket leak. I added a product called K seal to the coolant and the leak stopped after about 50 miles. I'm not normally a fan of such products, but replacement of the head gasket wasn't really an option.

Two thoughts:

1. Try checking for the leak as soon as the engine is warmed up. Then it won't be too hot down there at the inlet. If it gets too hot the coolant will evaporate. Had a somewhat similar problem with my 240 years ago. It would leak through the waterpump seal. Could only see it when the engine first warmed up. After that the cylinder head's heat would evaporate the coolant. Took me a long time to find that one!

2. Have you checked for leaks in other locations? One location for other Volvo engines to leak coolant is the small hose going into the coolant reservoir bottle. Also check for micro-cracks on the bottom of the bottle itself. Finally, thoroughly check the large coolant hose to the block. That one gets a lot of heat!