Dan's absence for many episodes were due to filming The Borrowers, Fallen, Blues Brothers 2000 & The Big Lebowski - the beard Dan has is for Lebowski which means there was a gap in filming or post production was starting & waiting for ADR work to let Dan return for last few episodes
Dan Florek previously appeared in a season 3 episode where he played Becky's principal.
Dann Florek also appeared in the big screen version of "The Flintstones" along with John Goodman. Florek played Fred Flintstone's boss 'Mr Slate'. John Goodman, of course, portrayed the enigmatic 'Fred Flintstone'.
Dann Florek plays Doctor Rudmen in this episode. Previously he played Principal Hiller in episode 3.9, Bird Is the Word (1990).