Sucks to hear that. I had a TS Astra that went a bit like that - independent mechanic didn't service to the book and omitted the timing belt renewal, a 60,000km/5yr interval item. If the belt snaps in service you'll destroy the engine so I was none too happy to learn about it; I was out to about 75,000km and 7yrs before I realised and had it rectified.
Maybe once your OBD tool gets here, you'll have a shot at identifying the intermittent issue since you'll be able to monitor it all the time when driving.
Of course the Subaru is the mechanic's recommendation, you have to service them 6-monthly!