You changed clutch and flywheel as you thought your clutch was slipping /on way out ...but refitted new items and still same ....then removed tranny to see metal filings in oil ?
Well assumption would be transfer box ....but the experts can reply :angel:
The centre hollow shaft out of the gearbox can corkscrew which splits the front diff casing. That would have been apparent when you removed the transfer box though. It's possible the front diff casing has split without the shaft looking damaged though. If that is the case then the car will drive through the viscous coupling giving the impression of a badly slipping clutch.
To check, take the transfer box off and look down into the front diff. Any damage to the front diff casing should be visible without stripping the box down