What bothers Me about the Glow Plug removal issue by a Mechanic is that they have no reason to be extra careful removing the Glow Plugs.

If one or more Glow Plugs breaks off the Mechanic will not want to try to drill out the Plugs because of the risk of damaging the Head. It is also more Money for the Mechanic if He gets the job to remove and reinstall the Cylinder Head.
So the win win is safety; remove the Head and let the Machine Shop take the risk for the Mechanic more Money.

There might even be an extra charge to take the Head to the Machine Shop.

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84 300D, 82 Volvo 244Gl Diesel