Sure, been there too!
Another thing you can do, is to download config file of the 600C and extract the the ipsec tunnel (phase1 and phase2) configuration and then upload it on the 100F(with the necessary adjustments) as a script. Or you can just paste it on a terminal when conected through ssh.
If it 1 or 3 tunnels I would waste any time and just rekey the PSK. I seen a lot of customer who would spend 6 hours trying to recover a key when they could just rekey the PSK on a handful of tunnels and been done.
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