Most folks have the turbo rebuilt if it hasnt had a catastrophic failure, usually a more economical solution.
Another avenue to explore would be a rebuilt from Volvo.
Some oil leakage is normal in these turbos especially if the engine spends a lot of time at low rpm, there are no oil seals on the turbine shaft, miniature piston type rings are used as seals, more effective @ higher rpm.
You will need a turbo mounting gasket kit to reinstall.
The aftercooler should be disassembled & the air side cleaned with varsol solvent until it rinses clean, blow dry with compressed air, be careful not to damage the fins, allow the aftercooler core to air dry for several days before reassembling. ( concern is a runaway engine on start up )
There is usually a small hole drilled thru the bottom of the aftercooler housing, the purpose of this telltale hole is to drain off any condensation during operation & also to alert the operator of core leakage, this hole must be kept clear.
If the raw water side of the core needs cleaning, I prefer ultrasonic cleaning, try the local rad shop or airport engine shop.
I am not sure if there is a aftercooler gasket kit or you have to purchase parts individually.
All o-ring surfaces must be clean & smooth ( no wire wheel, too rough ) imperfections can be filled with epoxy & smoothed
Use thick grease on o-rings, use a torque wrench & new lock washers.
Hope this helps.
