Hi Section8,
I've got the Quality Check plugin but it doesn't update (or correct) the file sizes
The other option you provided worked like a dream though!

I didn't realise you could drag directly onto the detail panel so that's something else I've learnt. The act of deleting first and then adding does indeed force a refresh of the size.
It's a bit of a pain to do them all one by one, but the solution works fine - just a shame there's not a one click to validate the size.
Anyhow a big thank you for your quick reply and solution