I've been sensing vibrations through the car body this week and assumed it was the wheel balancing or lost a weight from one of the wheels. Anyway I got home last night and as soon as I got out the car there was the 'sweet' smell of what seemed like engine coolant....I popped the bonnet and saw black oil under the engine mount and it was dripping underneath the car at the cambelt end.
Looks like the engine mount's hydraulic fluid has leaked out and my god the stuff STINKS


Now on the lookout for a replacement.
The symptoms are vibrations through the car at around 60/70mph and a slight lurching when coming on/off the throttle (more engine movement).
You can see the blackish fluid leaking at the bolt positions:



And under the car:

And in the wheel arch:

At first I thought it was the Power Steering fluid or Engine Oil but looking at it carefully and looking on line I found other similar cases to confirm the problem.
The fluid leaks out like a black oil and then evaporates/dries leaving brown stains.