Fujitsu laptop drive questions - pls. help!

Would be grateful for any help with the following Q's:

1. What causes a Fuji drive's head assembly not to seek -- the PCB is good, and the head assembly is not mechanically bound? Is it a sensor or bad head stack / preamp?

2. What exactly has to be matched to find a compatible head stack? Some say that all you need is model number & country of manufacture; others say firmware revision must match.

3. Are Fuji heads particularly sensitive? I tried swapping heads and when I put the original heads back into the donor (apparently) they were now bad. What are typical pittfalls?

4. If Fuji heads stick to one another after removing them, does it necessarily destroy the heads?

Thanks in advance.