End of Season 3 was the Ropers leaving for the spinoff

Season 4 brought in Furley and Lana and Lana left mid season

Season 5 was Suzanne Somers (Chrissy) salary dispute and not showing up to tapings and was only in 2 episodes of Season 5 then they brought in Cindy

Then Season 6 they brought in Terri.

Crazy amount of cast changes for the middle of the pack of the series.

True a lot of changes but not unique for a comedy of more than 4 seasons. MASH replaced Mclean, Wayne and Larry with David Stiers, Harry Morgan and Mike Farrell. And brought in Jamie Farr and a few others. And Cheers replaced Shelly Long with Kirstie Alley and brought in Woody and Bebe.

It was a few more

the bartender left from reagle beagle after season 5

Dean travers left after season 5