Thank you code. I've flashed the drive, and now the unit is reading much faster (and a little bit noiser) than previously.
Just for the benefit of other users of the same unit (Sony DDU1613, aka LiteOn SOHD-167T), I've used:
1) LtnFlash to make a backup of the original firmware.
2) 9S1B "stock" patch from codeguys to flash the unit.
3) KProve 2.4.2 in orded to by-pass zone protection, as well as for testing drive speeds before and after flashing it.
Thank you again