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I think there is a good chance it is a headgasket issue. You can pressure test the system to check for leaks in any other hoses.
Are the hoses hard when at operating temp indicating pressure on the system?
To rule out the head gasket, I would try a product called Blue Devil, I have had tremendous success in cases even worse than yours. It is a high end block and head gasket sealer. I don't know if you can get it there or not. Make sure you follow the instructions and chances are extremely good it will fix your issue permanently or at least for a very long time. They advertise a 90% success rate and a money back guarantee. Here is a link to the manufacturer if you want to read more about it.