Due to the different IBM labs and companies developing IBM portables and the time period over which they existed before USB, there are a lot of different types of IBM floppy drive.
Whilst we're only covering external here, there are at least 3 types of connector:
26mm / fattest: Found on the 701c
21mm: Found on the PS/notes, 850, 7xx tablets. 360, 365
17mm / Thinnest: Found on the later models which favoured optical drives built-in such as the 755CD, 760, 600 and various 3xx series. Ultraslim floppy drive.
21mm
This early floppy drive 66G5069, also known as "UltraBay Diskette Drive enclosure" actually contains the original multibay floppy within it's large outer shell. There are also fixed standard external 21mm drives.
These ultrabay floppy drives came in various models from various manufacturers, so externally each 66G5069 drive may look the same, but internally it could be totally different.
TEAC FD-05HG
Here we have a TEAC FD-05HG drive, which has one eletrolytic cap, which as far as I know should only be replaced with an electrolytic. I have had drive read issues by replacing these with a solid capactor. It's a 100u / 10v capacitor seen below:
You can get away, like I did with a 7.7m through-hole capacitor with the legs splayed outwards:
Whilst it's open you may (or may not) want to clean the magnetic heads with a little IPA and check the corkscrew spindle which moves the heads forward and back across the diskette is moving smoothly.
Even though this 7.7mm tall capacitor is longer than the original surface mounted cap, it still just fits under the floppy drive chassis - although you cannot go any more than this.
Sony MPF720-2
And here is another 1.44Mb ultrabay floppy drive - the Sony MPF720-2 (weirdly suggesting it's a 720Kb drive, but it's a 1.44Mb drive):
This Sony drive is similar, but you do not need to remove the little PCB in order to replace the 47uf capacitor:
In this case, small 6mm through hole capacitors with the legs splade are a good replacement:
