Small patch of rust - how easy / how much to fix?

The only way to fix that sort of thing properly is to cut out all the rot and replace with new metal. If the entire panel is available at a reasonable cost the normal way would be to either replace it or cut the required part from it. Of course a repair section could be made, but the labour involved might make this more costly than the above, unless the entire panel is very expensive.

It's specialist work which will need the appropriate skills. And beware of the fact that it would be easy to bodge it so it looks perfect - for a short time.

To have it done properly might well prove to be prohibitively expensive on a 12 year-old car.

Chris

It's verey expensive to do a proper job. Do what I do on my 15 yo Rover. Just clean it,maybe with sandpaper, and blow the right colour paint over it. Nobody will ever know and next year you do it again.

It already looks like the rust is under the paint realistically within twelve months this wll blow through.

You have two options either replace the panel or cut out the rusted section and weld another section in, you need to be able to access the rear area to prime after welding and apply a liberal amount of sealer.

which if it was something of real value might be worth doing. in the case of an old standard car it is not worth the cost and time, and the chances of doing it right enough to last ten years are low. a clean-up, knock back, fill and paint will be a sensible course to go along, and if it needs doing again in a couple of years very little has been wasted.

Thanks for the advice, I think this is what I'll do - as you say the car is quite old so it wouldn't be cost effective to do a proper full blown repair job.