Cleaning a used turbo, carbon deposits?

[Hoffbrohaus]

Bought a used turbo and just took off exhaust and compressor housing. There is no shaft play but there is a cap thing on the hotside under the impeller (propeller?) that has a scraping gritty sound. I blew some air in there and got little pebbles of black out of the crack.

Do I have to worry about this? The fins spin freely and fine. Any ideas how to clean it out without disasembling the cartridge and ruining the balance?

[Hoffbrohaus]

Just played with it again. It seems like that is a dust cap of some sort and when it's seated in the exhaust turbine it doesn't move and is fine.