Posted Sun Feb 26, 2012 7:02 PM
Iirc TOS uses the write protect mechanism of the drive somehow to detect a disk change, sounds like something isn't working there. The drive is free of dust and fluff internally I take it (long shot).
Most PC drives I've encountered do have the jumper, but it can be small and very well hidden, you might need to take the drives to bits to find it (they are usually labelled D0 and D1 (with sometimes D2 and D3 thrown in for good measure)). They can be hidden under removable metal shielding on the drive. Occasionally it is a very small jumper at the back, next to the floppy cable/ power. You can swap over a couple of lines on the disk drive cable to mimic the ID change I believe.