A clutch clutch replacement will set you back approx £180 to £220, depending on where you are in the country. It's definitely worth doing, because your cars worth about £500 with it changed out (depending on the model). As for the oil leak? It depends where it's from. Power steering pump? £350 ish, power steering box £250 ish? Engine oil from filler cap could be a problem with the cylinders, which means it's a right off. A leak from the drain nut? Might just be a new fibre washer needed, but of course, you'll have to change the oil out when you take the plug out! Don't panic though, any power steering leaks should have failed your MOT and if the mechanic say's it just needs done ASAP, it's probably just a little something that needs tightened up.