invalid node structure!

So recently my iMac G4 17" HD starts doing re-tries for a couple of mins and I run the disk utility and get an Invalid Node Structure error.

AHT showed no faults.

I have read that this is essentially a terminal hardware fault.

In the past I have 100% recovered the data from dead pc HDD's by replacing the pcb on the disk with an identical one (needs to have the same SW checksum).

Does anyone know if this disk failure is in the drive platter/heads or in the drive electronics?