Well, that escalated quickly.
The bushings at the front that the actuator arms mount to were actually not bad. One was a little sticky. With both arms off one shaft moves nicely, but the other is somewhat sticky. That left me with no option but to open it up, and see what's happening.
In the photo above I can lift the left hand set of flaps up and when I let them go they make a nice 'clunk' as they close.
The right hand set however, moves slowly and makes a dull sounds as it closes.
I've had a shot of cleaning around the flaps to ensure they are not dragging on any sticky residue on the insides of the inlet tract, and I've put some penetraing oil around the shaft to see if that improves it over time.
It has a trapped rubber seal, but I'm hoping I can clean that up and apply some sealant to re-make the seal.
Looking at it, I'd have to be brave to dimantle this any further as it looks like it would be pretty tough to re-assemble and get all the flaps nicley aligned.
Fingers crossed the penetrating oil does the trick.