1995 Chevy Blazer oil in radiator

I took my blazer to mechanic radiator leaking water-and running really rough -he replaced radiator- plug and said was running smooth-drove home 1 mile ran fine -drove to work next day 12 miles running rough as in repping up would not idle down- drove home- checked water in refill tank real brownish oily-took baster got out oily gook thinking they didn't flush out lines when put in new radiator-checked oil and transmission fluids both are full-scared to start it up noticed on one comment about bubbling noise behind dash maybe head gasket blown-i have heard noise for about year now - when had oil changed last asked man he said that is normal? Broen gook in radiator any suggestions and est. Cost to repair thanks linda