Lobster wrote:

The idea with any sanding work is to start with the coarsest grade you
need, and then to work up (down?) through the grades until you get to
the desired level of finish.

I've settled on the 80 grit for removing the offending black paint
marks. The 40 was too coarse, and the 80 is much better for this
delicate task. In practice, is the finish left by the 80 good enough
to paint on? It feels pretty smooth to me. I've only been sanding to
remove paint - the surface was fine before.

As an aside (and here I'm really showing how little I know about
decorating), the original was applied with a roller. If I touch up
with a brush, will it look obvious, or will it blend in relatively
well? The drips I'm touching up are around 5mm wide, so I'm not keen
to use a roller - seems like overkill.

Antony