Pretty easy to check if it's leaking.
If it's just starting to leak it won't be too messy. If gushing, the entire diff cover will be covered in oil. The bushing is oil filled to reduce NVH. If shot, there will probably be a clunking noise anytime weight transfer occurs.
Replacing with a solid bushing fixes the problem but introduces more NVH. It is a pricey repair to replace the rear subframe outside of warranty, so doing the bushings only is much cheaper. I'd expect harder driven cars to have this part fail sooner than those not driven as hard. Extreme climates deteriorate the rubber as well.
To the OP, why don't I see an alignment line on your invoice?
I do wonder why they replaced the drive shafts. Maybe one/both of the cv boots were torn.?
