No real easy way, the scan is not-too-good. One pixel magnified by however many times you applied erode. If you know where they are, paint them out first.
For speed. Back to gaussian blur, then Colors -> Threshold then the opposite of 'erode' Filters -> Generic -> Dilate.
For speed. Back to gaussian blur, then Colors -> Threshold then the opposite of 'erode' Filters -> Generic -> Dilate.