Are your floppy disks mouldy? Slide the metal over and check to make sure the surface doesn't have any small spots on them. I think your original floppy drive will work fine if you clean the heads. I've had about ten A500s come through here with floppy loading problems and every one of them was fixed by cleaning the floppy drive with a floppy cleaning kit. These things are old and dirty, and it's far more likely that the problem is simply dirty heads than chips going bad.
