I got a bad Western Digital WD4000KS Zeus for information recovery. As I have already mentioned in my previous stories, WD storage discs are not considered to be highly reliable. The printed circuit board is poorly protected of power unit thyristor effects, so chip of MHA and engine control burns out at any problem. MR elements of reading/recording heads are also very unstable and often fail out.
In that case the problem to user data access was because of a large number of sectors with errors and slowdown, a forerunner of a soon failure of one (or more) heads in the set.
To my great regret, the most part of unreadable sectors was in the MFT so I opened a hermetical zone in clear room and started to reanimate a half-dead head. Reanimation was a success (It is a rare case for Western discs), and all the necessary directories were recovered.