What you describe suggests that the floppy drive is probably OK now, with the new band, but there is a fault with the disk. If it's just one file, then you can get around this. Assuming that it's the data area of the disk, then just rename the file, and write a new version of the same file onto the disk, the old file, still there, will cuntinue to 'reserve' the possible damaged bit of the disk.
In case you're interested, the error message means that the format data is damaged, which might or might not incl the actual data. The fact that it will, after numerous retrys or restarts, read the data suggests the problem is marginal rather than total. The act of 'formatting' the disk writes a lot of markers onto the disk, in fact creating a lot of numbered/marked 'boxes' on the disk for data to be inserted into later. Hence the 'disk mark missing' error
Of course, if you got the system booted, you might find other files with a problem as well.
What version of LocoScript is it? If you've got SCRIPT.JOY this suggests an older version. I have an original system disk with that file, but it's not for sale or anything! But, if it's the right version, something could be done.
Do you have the CP/M boot disk? Your posting suggests NOT.
I have a Gotek drive, just sat here. Like you, I understand that it should be possible to get it working, but I've not YET bothered to persue this. As I have a fully working 3" disk A, and disks, and optional working 5.25 and 3.5" B drives, and 13 @ 8 Mb virtual HDs attached via JonB's uIDE add-on, I don't really need the Gotek.
Any way I can help get your Loco boot disk working?
Geoff