I have used 5w40 fully synthetic (halfords own) in mine for the last 4 years with no problems, but I am sure there will be a varied opinion on here.
Checked my oil the other day actually and had to top up about a litre, first time in the 8 years i have owned her I have had to top up like that, will be keeping a closer eye on her in the new year
I'm the same, but I've been using Halfords 10/40 semi synth oil for the last 5 years in my 180, no problems at all and no rattles or knocks.........I rarely top it up between oil changes. Despite being a cheapskate on the oil I usually get hold of a Rover oil filter on Ebay, I'm never sure how well made the others are.
There are loads of opinions on oil, but a lot of engineers believe that frequent oil changes using cheaper oil is better than long stints using expensive oil......especially if the filter is changed at the same time.
I also use Halford's Classic oil in My MGB GT V8, it looks a lot like the old Duckhams green oil and remains clean on the dipstick between changes.........I don't work for Halford's by the way !!