Inside-Out Boy! It was Clay Animated Bumpers Nickelodeon featured in the early 90's. I think there were only four clay shorts that I remember. Great Video BTW!
UPDATE: It would appear someone has finally found the missing Loretta the Letter Lady segment in question. You can watch it here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-qafahbnT77A.html
ANOTHER UPDATE: Well, I didn't think it was possible, but we actually found the Hall Monitor re-enactment that aired on U-Pick Live in 2004. You can watch that right here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-z8hClLG-r2Y.html