check the drop links first aswell as the arb bushes, both cheap and both on my misses fiesta gave exactly the same symptoms as you hear.
ARB are a bit fiddly but you DONT need to drop the subframe to change them regardless what you hear,grab hold of the ARB and push back and forth and you will hear/feel it bump about in the bush,there are two different sizes so get the right ones,i got mine from Ford and they cost almost the same as a motorfactors,plus i got the right size.(motorfactors sold me the wrong size,then me mate at ford put me right when i spoke to him)
Droplinks piece of piss in any case.

Just to be sure im talking about the same Mk what year is the car?

The heater,is the heater blowing only cold air? if so it will be the heater control valve, again check to which one you need as there was at least 3 different ones,one had a smaller outlet and can cause the car to overheat,one was just plane faulty(made by Ford) and one works fine. dont get one from a scappy as you might just get a duff one again, you could chance ebay,basicaly you pay your money and takes your chance.

http://www.zsoc.com/forum/showthread...+control+vavle
http://www.zsoc.com/forum/showthread...+control+vavle

just a bit proof to what i was saying