I think you are mixing up the A4000 Towers (but I could be wrong) from what the BboAh says, is that the Commodore tower had the Floppy Drive: 1 x Internal 1.76MB Floppy Drive.
The AT tower just used:
1 x Internal 880K (Actually a PC 1.44MB drive converted for Amiga use)
In this case, it is a Sony drive, which were notorious in that era for just dying from lack of use. We went though tons of them at my old computer shop, but they were dirt cheap also- I think back in '99 we were paying like $5 each if we ordered them by the case.
AmigaKit is probably doing the exact same modifications at AT was doing to their drives, so they are probably the closest thing to the originals as you will find.
More of an assumption than a mix up, the A3000T 040 came with a 1.76MB floppy drive, I just assumed the A4000Ts would also. But C= only made a small number of A4000Ts, so I guess the other companies that made A4000Ts (Amiga Technologies, Quickpak) only used 880k drives?
Shame about the Sony floppy drives. You would think Sony would make a higher quality product, but even back then they didn't! :-(