The turbo on my e250 coupe 2.1L diesel 2012 doesnt spool 90% of the time, and sometimes it randomly kicks in. I brought it to a mercedes specialist and they just changed the intercooler pipe as there was a crack in it. But said the actual problem of the turbo is much bigger and he's saying to replace the whole turbo.

I plugged in the OBD to read the fault codes and its giving me
P00AF72 (Boost pressure control 'A' has a malfunction. The actuator does not close.)
P029900 (the boost pressure of turbocharger 1 is too low.)

Does anyone know what could potentially lead to this problem?
Could it be a sticky vane?
Could a problem with one of the turbos cause the two turbos to not function?

I have attached a picture of what the obd is reading below

Many many thanks in advance!