Axle Boot & Torque converter seal

The axle boot protects the CV joint inside. The CV joint is filled with balls, cage, and grease. If the boot is cracked, grease can be washed out and dirt can get in...damaging the balls/cage. Signs of a bad CV joint would be vibration and noise.

Now, CV joint / axle can be rebuilt. There are shops out that can do it. When I did it 15 years ago, it was about $100 per axle.
Or you can purchase a rebuilt CV joint / axle from PartSource/Canadian Tire.

And I suspect they were referring to the seal where the inner axle meets the transmission. This seal can be easily replaced when you have the axle out. The seal is like a $5 part. If you are replacing the boot/axle, I recommend you replacing the seal at the same time...even if the seal is good. You are already there.

The only way you know for sure is to get a 2nd option from another garage. If no damage to the balls/cage, you can just replace the boot.

Axle boot is worn... is it leaking?
Torque converter seal needs to be fixed... is it leaking?
I'd go for a second opinion and have the mechanic explain to you why and if they need to be changed.