After doing some code archaeology, I am pretty sure that wkey records were never actually used. I am unable to find any point in time where wkey were even able to be written to disk. So it's really odd that you have a wallet file that contains wkeys.

In any case, wkey is supposed to be a private key with some extra metadata. There should be a 4 byte version number, followed by the private key, followed by an 8 byte creation time, followed by an 8 byte expiration time.