Set Square wrote:

Unless the skirting needs to be anything fancy - and therefore
expensive - replace it, particularly as you're re-plastering. You'll
probably damage the walls getting the old stuff off if it's nailed on
in the conventional way - but the plaster will cover the damage.
Stick the new stuff on with Gripfill, and fill any slight gaps along
the top with decorator's caulk before ** painting.

Pre primed MDF skirting is the way to go IMO. No knots to seal, no twists,
stick it on, caulk and just a coat of gloss.

Dave