Just to make it clear, on all
VB flights there is a preflight walk around, the pilots are required to do a walk around prior to every flight but are probably only allowed 10-15mins for this. If there is a PPU (power push back unit) it would be an engineer doing the push, once again due to
VB's short turn around there is only about 10 -15 minutes to do a walk around.
You may have seen the bag boys doing a walk around prior to a flight, unfortunately these guys are only trained to drive the tug, plug in a headset to speak to the crew and tell them the chocks are in. So any walk around performed by a bag handler would only be looking for the obvious things i.e. refueling panel closed, engine oil panels closed (although wouldn't check the oil fill cap is on), holds are shut and so on.
But despite all this, if there was a obvious sign of corrosion on the nose landing gear this would have most likely been noticed by the R&D bag boy.