BillFitzmaurice.info

I had a panel separate during construction of a WH8 (the bottom from the bottom back) First time PL has ever failed me
The brace is still intact but, the panel seems to have separated even below where the brace is. The PL was cured plenty so I'm guessing it separated because of all the trial fitting of the horn in the shell.
Can I squeeze some more PL between the panels, fasten well, and rely on it or does it need to come off and be cleaned up? ugh.

You should be able to fill it. I've never had a PL joint fail, but I do not fool around with a joint until it's fully cured. It gets its strength from its expansion, and if you upset that expansion before it's fully cured the bond won't be what it should be.

Get a knife and scrape out all you can.

I haven't tried it myself on PL, but a hot knife and heat gun might work even better; just be sure to have a good ventilation fan to remove any fumes / smoke.

This is common for removing aliphatic resin type carpenter glue.