Lock ring

The main shaft lock ring is of aluminium, and digs itself into the bearing it rests on. You can notice this from the returning vertical play in the main shaft. I had turned the lock ring already around, but after a few months it had itself dug in again. The bearing was broken as well. I'm not sure in what order, but I think the alu coming from the lock ring went straight into the bearing...
I now sanded the lock ring flat, and put a flat steel washer between the bearing and lock ring.

Worn main shaft lockring. It digs itself into the bearing it rests on.

This stuff came out of the main shaft top bearing alone!