Thanks Deano, you have answered a question that's been nagging me for the past 5 years.
My engine went bang, well it didn't go bang, more like a loud thud thud thud noise, when it happened first thing i did was to look up as i thought it was a low flying helicopter or something...
Turns out it was a chunk of metal in the number 5 cylinder. was pondering where the **** it came from. Strange thing i noticed upon stripping the engine down ( apart from the halfords ratchet handle in the "V" of the block) was the 2 different date codes on the turbos. Thought one has been replaced.. but why.
Looks like mine had the same fault as your did, but the f**kwits who did the repair never bothered to clean out the mess. Just sell it on quick (to me) So the nut eventually found a new home at the end of the spark plug.
Count your lucky stars mate, your engine could of ended up looking like this ....