I just had the gearbox from my '88 R 100 refreshed. Five new bearings, seals and circlip upgrade. It has 81,000 miles so while the transmission is out, it is a good time to replace the clutch.
The friction plate measures 5mm.
That said, when replacing the clutch, besides the friction plate and pressure plate, must the carrier plates also be replaced? If so, help me understand why.