Well, the sc unit repairs were completed this morning and it is back on the car and that sweet whistle is back!
Found another issue while the belt fluff was being clean out. One of the new bearings had lost it's seal when the belt let loose, so had to have a new bearing replaced as well.
Will be running it sedately until the weekend to allow the belt to bed in properly. Should have more than 500 kms on the belt by then with a mid week trip to Bendigo.
The pic below is the total amount of belt residual that was recovered from inside the sc transmission housing:

It also shows the bearing that lost it's seal. It was exposed to some of the belt fluff so better to replace it.
Total repair bill is 7 hours of labour plus a belt and a bearing.
Some points to note:
1. Regular inspection of the sc transmission belt is needed, suggested by the guy who did this work (Barry) at least every 3 months. Replace belt if any visible signs of wear or tear. Can be inspected via the top air outlet and rotation of the pulley.
2. Regular inspection of the cooling fan that supplies air to the sc transmission. Noticed that it was not flowing the air too well and was partially blocked.
3. Recommended SC Transmission belt to be replaced annually, from both Tim and Barry.
Still in the dark as to why this belt let go. And unfortunately, it will remain a mystery...
