Sorry, MG.
My Petco rats used to have a lot of health issues, especially respiratory. I even lost one within the first week - he was just a little baby, and so cute too.
With the last few rats, I would try to "rescue" one from a reptile shop. The ones I've gotten from there were usually very healthy.
And, apparently, I'm a moderator again elsewhere. Not sure how that happened. I signed on to check a news article, and yeah... hopefully, I'll be removed again soon, because I don't have time nor desire to deal with any of it.