I think the guts are different.
The sag is usually a spring inside that I've read is not the same as the spring in the doors.
On mine some of the sag was a worn square hole in the guts, and swaping that with another fixed some of the sag, but not the spring part. I'm wondering if a spring shop can make new ones, but I've not asked.
I should ask, because two of my brothers work at places that make springs...
