For anyone else in this position, after hours of searching, I've found info.
You need to remove part of the exhaust, then the under body panel to remove the selector from underneath the car.
Details here Volkswagen Workshop Manuals > Golf Mk5 > Power transmission > 6-speed manual gearbox 02Q > Gearbox mechanics,operation, construction,diff. > Repairing selector mechanism > Removing and installing selector mechanism > Removing
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