The Diff on the rear of a T4 is hung on two crossmember that span between the two rear arches. They're in a pretty vulnerable position and as a result we see these crossmember rotting regularly - quite often leading to people thinking they need to find replacement.
There are a few variants of these crossmembers:
Where possible here is how we deal with this issue.
The crossmembers are split in two - the upper and lower halves are separated by drilling out the spot welds holding them together. The upper folded half can then be sandblasted, repaired as necessary and mated to a replacement lower section. We have these laser cut and can supply them if required.
These parts can be ordered here.