It is quite a saga. I had difficulty to start the saw running. someone recommended me a motorized tools "repairman" which was a disastrous move because after the saw was at his workshop for two weeks without being fixed, I took it back and today I found that the engine's starter cord can't be pulled, I guess because the engine is stuck. I don't think that going back to him will solve anything, he for sure will deny it and nothing good will come out of it.
Since you've mentioned the option of using cheap chinese engine - I would like to ask again if you have any experience with these engines? let me be more specific and note that the saw is used only every once in a while in my garden. it's not intended (at least at me) for professional use.
One more thing - do you or any other member can guide me to where I can find the workshop manual for the Stihl MS180?