Well, I have not tested all available floppy drives for the Amiga range, and I sure others might have different opinions, but in my personal experience the Chinon FB-354 (provided it comes with a cover that fits; please be aware that I never had an A4000 and I therefore don't know the requirements) is very sturdy, easy to maintain and cheaply available (hint, hint - spare parts, especially springs for the mechanism, hint, hint). I bought all my drives on ebay. But again, never for the 4000. However, I'd guess that any drive offered for the A4000, as long as it's a DD drive, would do. If you had a way to find out if the height of the slot is identical to the A2000's slot (my guess would be that they are the same), drives for that machine - duh! - would fit as well. Electronically there is no difference.