Swapped out the guibo (again), re-set the preload on the center support bearing, and turned the front rotors (again).
I replaced the differential back on April 8th of this year with a Z3 limited slip inside a E21 case. I also replaced the transmission mount while I was down there.
After the differential replacement, and the transmission mount replacement, I encountered a slight vibration at around 2500rpm, but it became violent at around 4000rpm.
I had a factory E21 transmission mount in there, and that thing split in half after about 68,000-miles of use. So I replaced it with an AKG transmission mount. Worst mistake ever, it was sending a tremendous amount of harmonics through the drivetrain.
I thought it may have been an issue with the improper preload on the center support bearing, so I changed that a couple of times, to know avail.
I contacted Blunt and purchased another factory E21 transmission mount, that helped out a ton, but I was still feeling a little bit of vibration going through the drivetrain.
With about 16,000-miles on this guibo, (they typically start the show cracks around the 15,000-mile mark), so I swapped it out for a new one. I also re-set the preload on the center support bearing, that seam to take care of the harmonics that was going through the drivetrain.
The last photo is the list of all the times that I replaced the guibo since installing the S14.