Told front and rear differntials leaking. $4,000. to fix. Loud grinding noise on heavy acceleration. Is this price correct?

Thanks. Also want to pass this along that I read somewhere on the Internet. My engine lights on and I was told it's my catalyst converter so it won't pass inspection. I was told to call the Cadillac dealer to see if the catalyst converter was still under warranty. They said yes so I'm bringing it in on Monday. It's warranted for 12 years or 200,000 miles. I literally just made it. Unfortunately, differentials are way out of warranty. I didn't see the SRX model on carparts.com

The SRX is between Deville and STS on car-part.com