In my experience, it's quite normal for the turbine to continue spinning for about 20 seconds after the engine has been switched off. If my car is up to operating temp when switched off, the sound is barely audible. If the engine and turbo are cold when switched off, it sounds somewhat rougher/louder which is also apparently normal. If the sound is a grinding noise as opposed to a free spinning noise there may be issues. The turbine should spin freely by hand. The middle of the turbo is essentially a shaft with a fan either end with a bearing pack in the middle. Watch this vid from about 3:30 to see what I mean
The bearing pack in the middle is the part will usually fail, which can eventually damage the intake and/or exhaust housing. The main culprit usually being a clogged filter in the turbo oil feed line. If your turbo is found to be stuffed you must check/remove/replace this filter or you will quickly damage the new turbo. You'll find a million threads in this section about this issue. I had the filter removed and had ETM's replacement oil feed line installed for peace of mind. http://www.fordxr6turbo.com/forum/Replacement-Turbo-Oil-Feed-Line-t45049.html&p=668494&hl=replacement%20oil%20feed%20line&fromsearch=1#entry668494 I would think you would need to bring the entire turbo over for assessment. Another thing to check is to see how much play the turbine shaft has by grabbing the nut on the intake side and wiggling side to side and in/out. A millimetre or so side to side should be ok, but movement in/out can be a sign of trouble. To answer your other questions: The stock BF turbo is Garrett GT35/40r, and you could replace it, or they can usually be rebuilt to save money if not too badly damaged. I'm not sure about suppliers/reconditioners in the Melbourne area, hopefully someone here can recommend one.