When I took my 2008 Subaru Forester to my local mechanic for a service it was running fine, but one week later the car jettisoned all its oil. The mechanic told me a cam seal had failed due to high oil pressure caused by a faulty oil pump. It cost me $1100 all up with a new timing belt due to the oil spraying everything. I then noticed that it was using more fuel than usual, and a day later the engine started running really roughly. This time he tells me it's got a broken camshaft! I know I'm being screwed over, but I don't know how to proceed. I am convinced it all goes back to that initial service. It could end up costing me thousands! Thousands I haven't got.
It might or it might go back to what the mechanic did or didn't do at the service, but there's no way to tell, so you're stuck with getting it fixed. Find a Subaru specialist and take it there if you have lost confidence in your mechanic.