[RacebyDesign]

With manual transmissions there isnt the same heat/contamination level as with auto trans. Still, spirited driving can leave metal shavings over time.

90k intervals are fine but you could service it sooner and not feel guilty (especially if driving it hard) Oil is always cheaper syncro's. Assuming your driving it responsibly I wouldnt worry about your current service schedule.

After the first trans service I would keep an eye on the fluid every few oil changes. Cars in the 100k+ realm tend to dirty their fluids quicker than new vehicles.

Current service department standards (at least Ford dealers) are recommending auto trans flushes at 30k and manual trans drain/fill at 60k regardless of trans type. This is definitely more conservative than many of the owners manuals but fluid changes are high profit margin services and being over-protected is a safe approach.

Added protection of high-end fluids from Royal Purple, Red Line, Motul, etc can definitely help in severe cases.