But 8,000 miles is pretty good going for an oil change.. .
Having said that, when I was a lad cars had carburretors! (ask your dad)
In this weather, particularly if you do trips of less than 10 miles, the oil won't get very hot.. so any condensation, acids and carbon are not getting as burnt out of the system as they might in summer - the oil is earning its keep at the moment.
The beast will also be running on a "rich" setting for longer than when the weather's warm.. so you will have more condensation, acids and carbon in the oil in the first place..
I'd say "go with the flow" and humour it a bit.
Get some decent 10W40 semi-synthetic from Halfords (their gold can for diesel stuff is pretty good) buy a genoooiune parts oil filter and give the beast an oil and filter change.
The old stuff goes down the tip, not down the drain.. and all you have to do is get that light to go out. Dunno if it's a dealer reset or if it goes out by itself (dealer reset would drive me bonkers though.. quite why I like my cars with carburretors!

)
Ralf S.