In this business a month is like a day - but if you want to send the revised version, you could certainly send a quick note that says something to the effect of "I just started saw something that needs fixing. I'll get this to you in 8 weeks."
Always make sure to reply to the e-mail chain so if they forget you, they can see the history of the conversation.
The main thing to remember is - the agent wants your book to thrill them! They are on your side. They want a book to fall in love with - because they are going to have to work on it, for free, for a long time. So be nice to them and they'll be nice to you.
From Elephant's Bookshelf Press
by R.S. Mellette
"WOW. That is the first word that comes to mind when I think about how I felt reading this book - WOW. I was so pleasantly surprised - oh, let's be honest, it was more like blown away!" -- Holy B. In NC, Amazon Review.