check emissions system warning light caused by Glow Plugs

[HAMISH MCC]

Hi Forester owners, I have a 2015 Diesel Premium Forester, bought from a Subaru dealer up in Beauly (it was their demo car) and its a great car BUT I have the Emissions Control System Needs Checked warning light coming up. I have put an OBD scanner on it and got the code P067A (Glow plug No4 circuit low voltage detected). The plugs themselves are only about £30 each however I understand they have a tendency to snap on removal. Has anyone had a go at this repair or had it done by a dealer? If you tried it yourself how did it go and if you got the dealer to do it how much did they skin you for it? Lastly has anyone ever seen a Haynes Manual for the diesel models?