when vauxhall wont entertain a insignia for a known common fault 4 months out of warranty think you will struggle with one thats probably been out of warranty for 2 years !!

Seems you have no mechanical experience so i suggest you ask a few friends what garages they trust or find a local diesel specialist and let them take a look

Dont know if its just my area but most dealership garages these days seem full of young lads 18 to 21 and maybe one master tech looking over them and they just want to fit new parts til problem is solved !! ive just had a friend with a Audi thats been in twice to Audi and mis diagnosed on both occasions came to me and we had it sorted with in a few hours