Filter white specks with Avisynth

I've got a video that is not bad except for white dust specks.
Colour, 464x352.

I'd like to remove all the 2x2 or smaller white spots that last just one frame.
E.g., as image, top right.


I tried the RemoveDirt() AVSI, but while it gets rid of the spots it destroys too much detail. Even extreme sharpening after can't restore the original detail.
It's very good if you have a crappy source, but is overkill for this.

Is there a different filter that is more specific or does less collateral damage?
Or a tweak to RemoveDirt -- the "repmode" perhaps? This doesn't seem to be documented though.

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