Welcome

Link to maintenance manual library:
Model 124 Maintenance Manual Index

I would also check the following to get yourself to a baseline before playing with the turbo:
Suspension links front and rear, ball joints, control arms, etc.
Flex disks in the drive shaft - it is ugly if these let go
Brake hoses - safety first
Vacuum lines - replace them all on principle with fresh tubing and connectors

Injectors - contact forum member greazzer, he rebuilds them for a reasonable cost. He's located in Columbia, SC.

Fix your profile (under user CP) and put in your location. There are members all over the US that can help out.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech