The oil is very clean - so I'm thinking it is from the gearbox rather than the engine.
It's dark at the moment, but looking underneath with a torch I have located that it is dripping between where the sump plate/under engine skid plate finishes and a black torsion bar that is almost level with the back of the front wheels. The area above there is coated with oil so it is difficult to determine where exactly it's coming from.
Looks like an up on the ramp job for my local indie.
I'll try and take a pic tomorrow in the light anyway. But does this sound familiar to anyone, or indeed, expensive?! (Silly quetion - everything is expensive on these).
