I plan to change the oil and filter on my Mk6 Fiesta this weekend. I remember the Haynes manual said to check and renew the O-ring washer for the sump plug if necessary but it didn't mention anything about renewing the plug itself. A few sources say to renew the sump plug for each oil change. Is it better to be cautious and change the sump plug?

I regularly re use the sump plugs with rubber o ring in them, never had a problem yet unless they have been damaged then I've replaced the complete plug/washer.

For what it costs I'd change the complete plug.

You can reuse it, but ideally you would want to change it at every change, they are crush washers and are single use, I have reused mine once - just remember that if it leaks and needs replacing then you need to drain all the oil out again just to replace the O ring worth a few pence.

Btw, also look to change the fuel filter as well if you haven't, makes quite a difference :)

I could get a new rubber washer from CarParts4Less for 12p. My local GMF has a Corteco sump plug and washer for £3.60. I've changed just the washer before but I wondered if perhaps plug itself should be changed as well because the threads look prone to damage.