Stuck on 99%

I have washed every square micrometer on this fin spine multiple times. I have used 2.6 liters of multi-purpose cleaner, on top of 4 liters of stone cleaner. I have used every attachment and every extension. It is not cleanable. Any suggestions?

I have washed every square micrometer on this fin spine multiple times. I have used 2.6 liters of multi-purpose cleaner, on top of 4 liters of stone cleaner. I have used every attachment and every extension. It is not cleanable. Any suggestions?