Thanks for the suggestion.
Here are the results of the commands, run in order:
~ # vmkfstools -i /vmfs/volumes/510fedc8-5b3be36a-3be0-001a6424a942/wcvmvi01/wcvmvi01-000002-delta.vmdk /vmfs/volumes/510fedc8-5b3be36a-3be0-001a6424a942/wcvmvi01/wcvmvi01_new.vmdk
DiskLib_Check() failed for source disk The file specified is not a virtual disk (15).
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~ # vmkfstools -i /vmfs/volumes/510fedc8-5b3be36a-3be0-001a6424a942/wcvmvi01/wcvmvi01-000001.vmdk /vmfs/volumes/510fedc8-5b3be36a-3be0-001a6424a942/wcvmvi01/wcvmvi01_new.vmdk
Destination disk format: VMFS zeroedthick Failed to open '/vmfs/volumes/510fedc8-5b3be36a-3be0-001a6424a942/wcvmvi01/wcvmvi01-000001.vmdk': Input/output error (327689).
So it seems the 000002-delta disk is the problem child.
Anything else I can try?
Thanks!