Just put "turbo rebuild" in the search box for youtube.com and watch a few.

Klaus
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Always willing to listen, just not able to take direction.

If you did an engine swap, you know how to use PBblaster and take the turbo off. Not a difficult job. What is surprising is that the turbo itself has failed. The new, modern units are normally quite good and not failure prone like the 740 version.

Turbos can be re-sealed on your work bench. All you need to know is the size of the turbo. Only if the bearings on the center vane are shot is the turbo dead, and then it should make a lot of noise.

A little oil in the intake is normal. Oil getting past the oil return line and leaking down the engine is an easy fix. A new blow off valve or anything external is easy to do. The only real maintenance is to keep the PTC nipple clean so that the crankcase pressure remains negative at all times.

Klaus
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Always willing to listen, just not able to take direction.

Can't help much with the repair (other than it is low pressure so should be easier to repair than high pressure), but as a tall guy with the original model S40 they are small and too low on the ground for a family car but fine for a single guy. Feel a bit sporty (despite slow). We have the early non-US model with MAP ECU which is reliable and very easy to maintain except that only a genuine Volvo code reader works on them. Engine repairs are hard because of limited space.

Something I found out recently is how aircon has evolved. The latest models are much more reliable and efficient in that there is no clutch. They run all the time, just have a linear bypass valve from high pressure to low pressure side (not just on/off but regulating). This means it always keeps things lubricates and should last longer. However I do not know when that was implemented other than some manufacturers started with it around 2001. If you want to comfort yourself that you are buying a good car, it will be an advantage if there is no compressor clutch. You'll see the compressor pulley turning all the time. The modern compressors of the mid/late '90s used on VW and a number of others were troublesome, sometimes lasting less than 2 years. They had a mechanical regulator internal to the compressor but still a clutch. Expensive repairs if you want to maintain the aircon.

My 2L non-turbo struggles with any load, even only 1 or 2 passengers. Driver-only is fine though. Turbo should help. Brakes are great, no excellent.