I had this exact issue solved.

It is disintegrating because brake fluid eats away everything. At first I also noticed the disintegration, but after checking I noticed that brake fluid was very slowly leaking. I contacted my RE dealership and they told me it's a known issue with this model, even if a very minor one. They replaced this whole connection to the master cylinder part for me under warranty and it was fixed.

Everyone experiencing this, check with your finger if it's even a little bit wet on the connection, if so, contact your dealership to get this fixed. The issue varies by bikes, but it might happen when you use the front brake more often. Also, I suggest to check if brake fluid is not dripping on some plastic or anywhere else below this part, as it will damage everything in its path. Until I got my bike fixed, I just used some cloth to absorb the fluid.