Season 9, Episode 24 "The Case of the Fanciful Frail" is a remake of Season 2, Episode 15 "The Case of the Foot-Loose Doll" which is an adaptation of Erle Stanley Gardner novel of the same name:
"The Case of the Fanciful Frail" features an instrumental of the song "You Need Us," which was sung by the Honeybees on "Gilligan's Island: Don't Bug the Mosquitoes" (1965).
And the same song, using the second verse, replacing pronoun "us" with "me" from the title, is used by MeTV to promote their programming:
and finally the original song from Gilligan's Island:
And, finally, the song made a cameo in another "Perry Mason" episode "The Case of the Golden Girls" that was a take off of the Playboy mansion versus prescient foreshadowing of the sitcom by the same name: