I had to change out my TGV's because they kept getting stuck closed (no boost).
When they came out the turbo side was all caked in fuel/oil mix.
My assumption is bigger than stock turbo and excess heat caused this build-up.
If you are stg3+ might as well get deletes and program those codes out too.
May gain +1hp for your efforts too
Make it idiot proof and someone will make a better idiot.