Its dirty, flakey...and it may have sent the turbo south. But what is it?

[jmscdgn]

MVS community,

I recently replaced the turbo cartridge in my 740t (TD04 13c) due to leaking oil, and considerable shaft play, and noticed a lot of hard but flakey crud in - and around - the hotside/exhaust turbine wheel - photo attached.

I've also seen a similar crud inside the valve cover - 2nd photo attached - which is similarly flakey, removable with a fingernail, and was hoping for some experienced eyes to diagnose whether these two things could be connected? what the source of the crud might be? (mainly under the valve cover)  and what the best course of action would be to prevent further build up.

A compression test (dry) done on all the cylinders reads 155,160,165,160, and engines done about 133000mi. I've been running full synthetic, and high octane for the last 4000 miles, what it had before that is anyone's guess...

Insights / opinions much appreciated,

Thanks, and best wishes,
James