One of our local garages has a reputation as the safest MOT inspection garage in town and I am reluctant to change it. However they do not use Dexos 2, they use C3 fully synthetic.
I only do 10,000 per year these days but I am happy to do an annual oil change is enough for me, although the service manual says that a Dexos 2 service interval is 2 years.

To confuse things further the local Vauxhall dealer service centre recommend a yearly, not 2 yearly, service even for Dexos 2, and also info