Floppy Drive in Apricot FP (Portable) dropping tracks

[roddersuk]

I've recently bought a Greaseweazle as its such a useful tool for retro enthusiasts such as myself.
I've been working on restoring an Apricot FP (Portable) and the floppy drive (a Sony OA-D32W-90) isn't working, the BIOS reports an error 35 which suggests the FD isn't responding. I've given the drive a service but no joy. On power on the heads do move to track 0 so at least that's encouraging,
I've been using the greaseweazle to try to understand what's going on and found that the heads are not moving correctly.
If I try to move to track 79 the heads only move about half way across the disc.
If I then request a move to track 0 it doesn't move all the way back and gw raises an error because the track 0 sensor hasn't been triggered.
If I try to read a disc it fails reading track 1 as the track 0 sensor is still active (presumably because it didn't move the heads).
If anyone can shed any light on what the problem might be I'd be grateful.
I'm hoping that its not a faulty stepper motor as these drives are like hens' teeth!

[roddersuk]

On checking the rpm, gw reports a median speed of 944 which is way off from the rated 600, but it really doesn't sound like its going that fast. Does gw handle drive like this that operate at 600rpm out of the box or is there some configuration i need to do?

[roddersuk]

I came across a comment in one of Adrian's Digital Basement videos that suggested that stepping too quickly could cause steps to be missed on early drives. This is a very early 3.5" drive, is there any way to slow down the stepping speed in greaseweazle?