A V-block is a precision locating tool: its two machined faces meet at a fixed 90° groove that cradles round or cylindrical work so it can be marked out or measured about a true centre line.

The whole usefulness of the block depends on that V-form staying geometrically exact, because any job seated in it inherits the accuracy of the seat.

When the contact faces wear, the included angle and the depth of seating change, so the workpiece no longer sits on the correct centre height or axis.

Every mark, height or measurement then taken from the block is shifted by the amount of wear, quietly spoiling the accuracy of the finished job.

Ignoring the wear lets these errors continue; increasing clamping force cannot restore a lost angle and may bruise the faces further; painting only hides the defect and adds an uneven layer.

The correct remedy is to regrind the faces back to the true V-form (recondition it) or, where wear is too deep to grind out, to fit a new block.

Hence, the answer is Replace or recondition the V-block.