Noticed a burning smell the other day and after a quick look over the car it seems theres a bit of an oil sweat coming down between the gearbox and engine landing on the cat.
I havent had a chance to jack the car up yet, and cant see where its coming from in the engine bay, is there any common places that leak that could be causing this?

Cheers,

 

Yes its either the slave cylinder leaking so keep an eye on your brake fluid level or its the Crank shaft oil seal, both jobs require the box to be removed, i would say its the crank shaft oil seal, which is a flywheel off jobbie. Mine was weeping on my ST170 so i changed it along with a new fly wheel, clutch and slave cylinder.
If your going to take the box off i would replace clutch and fly regardless of age

Second thoughts check your thermostate too, these can leak when the engine is running and the coolant leak may make its way on to the cat, but if its 100% oil its crank shaft seal

 

Pretty certain its oil, ill take your advice and do the clutch at the same time.
Whats the reason for changing the flywheel? Cant clutches normally be replaced on there own?

 

The st170 has a dual mass fly wheel which is a serviceable item so they wear out. unfortunately not cheap at around 450 for the fly alone. clutch slave fly and crank seal should set you back roughly £800 at a garage

 

Is that a fitted price or just for the parts? I would do the work myself.

 

That is a fitted price, when i looked into getting mine done at a garage it was an entire days labour to have the job done. Ford quoted me £1250 Fitted, cheapest i could find was the £800 (including import tax) so instead i spent £800 on importing a solid lightweight fly and stage 3 kevlar clutch and new slave cylinder and fitted it all myself. Fit and forget and the fly will transform the car.
I did the job over a weekend and refurbished my hubs, shocks calipers etc whilst i was at it, probably could have done it in a day.