The point is that the problem is not a performance one as such. Most people don't like the upshift delay, I hate it on my 540i.
If you have verified that the line to the unshift vacuum element doesn't hold vacuum then you have found the problem. It could still be a hole in the line or it could be the line disconnected from the element but if it doesn't hold vacuum it can't do the function and the controller recognizes that fact. To satisfy the controllers desire, one will have to fix the problem.
I wouldn't recommend this job as the cable has to be attached inside the trans and both the basic asdjustment (for shifting) and the upshift point adjustmenthave to me made after installation.
Either that or manually shift it for the first time interval (not sure of that interval)
Bosch Master, ASE Master, L1
33 years MB technician