RE: Risa'a weight problem
Way back in the thread, someone pointed out that they taped 4 episodes at a time (one day, once a month).
So episode 5 is only one month after episode 1. Risa put on all that weight in just one month.
One of the screen caps shows that. I wonder if it was the stress of being on TV that caused Risa to over-eat?
RE: Muscats who stay - Muscats who go
There is an episode in which they do a 'Complain to Kobayashi' segment.
KONAN complains about something. I'm not sure what exactly (damn, my crappy Japanese listening comprehension!

)
But Kobashi shows KONAN a kind of audience appreciation/reaction chart.
As far as I remember, Acky rated best. I think KONAN rated zero - or something like that.
I'm
not saying that audience reaction was the only factor in whether a new member stayed or left, but if a new member caught the audiences' eye, and there was a favourable audience reaction, then it is logical that she was more likely to stay.
There could be a million reasons as to why members stayed or left. I'm sure some girls appeared for no other reason than a few of the OG muscats were absent and the production team needed a few extra girls to make up the numbers on that particular taping day.