a friend of myn traveled through Croatia and the manifold exploded off his transit. At that moment he felt utter dispare. No parts network no dealers no help. Until a local happened along and directed him to "Mr mechanicals" who displayed welding and fabrication talents that left my mate rather spell bound. This was about 8 years ago but is should give you an idea of what they are up against.
However, to me, it should be fairly obvious that blockling off that oil way is never going to work and the oil needs to be cooled in that water bath for a very good reason.
I dont know what help you have in Croatia Bojan but i am certain you will cost yourself more money in the long run by not fitting an oil cooler, do it as the maker has done it, and save yourself a some money.
We may moan about our dealers in the uk, but at least we have them, (you may argue the Croatians are better off but thats another story) i dont suppose our scrapy members have one spare? I imagine it makes selling an engine impossible with out one.
How to help the guy? Anyone?