I'm looking for some advice please.

I have a V70r I bought with issues, one being a mystery water leak. Oil/water mix and exhaust gas in coolant suggests head gasket area. No cracks in liners evident and it's been shimmed.

Head off and back on with same issue but it is evident that the block has been machined, leak not cured. Plan is to now is to strip and rebuild with addition of hermatite.
I used genuine Volvo gasket and torqued down meticulously.
Question is should I only used genuine head gasket and the panels thoughts on the additional hermatite or similar?
Thanks a lot.