Full service at my local garage includes an engine oil flush. Apparently they drain the oil, put in a flushing oil, run it for 25 minutes, drain the oils and replace with ordinary oil and a new filter. Of course this an extra charge which I am not overly concerned but what does concern me is that there are many people "out there" saying an engine flush can do more harm than good and no regularly serviced engine should need it. Also Subaru do not recommend it but I can't get that answer from Subaru. Should I or should I not???