[jclark003]

It's certainly possible fumes entered the cabin if you were idling with no propulsion. Wind could have helped make things worse.
If you suspect a leak check up high by the turbo flange where the exhaust riser/mixer elbow connects. A leak lower in the system would most likely cause significant flooding. if you start the engines you may be able to feel exhaust pumping out. Some engines use a crush ring between the turbo and exhaust riser. Possible your talented mechanic disconnected at this point and did not replace ring/gasket.

You may want to check for fuel in the bilge spaces. That can account for a lot of diesel smell too.

Sorry to hear so many problems. Time for a new mechanic.