Yup I had this repaired while I was on the road. Real big learning curve for me about how a a parking brake works on the Ford E450. :(
The parking brake is part of the driveshaft AND when I said since it was only leaking a little and said I'd wait to have it fixed the mechanic told me that that part holds a substantial amount of your transmission fluid. And if that parking brake assembly goes I'd be dead on the road with no transmission.
I took mine to a semi-truck repair shop and waited for it. And it was no where's near $4,000 like the poster said in the link you provided.