Lovely trio. I've been playing for over fifty years now and have had all the usual suspects, including Wal, Alembic, Spector, Dingwall, etc. overwater basses are the hands-down winners for me. Enjoy.
My guess is your trussrod is loose. Sometimes a firm dunt with the heel of your hand to the neck around the 12th fret is enough to sort the problem. Don't hit the neck so hard you break it though!
That looks great. You pay a fortune from the Fender Custom Shop to achieve that finish on a neck. I'd leave it; it's part of its history. Good luck if you do decide to go ahead. This reply will bump your post back up the line again, allowing more folk to read it.
The last time my truss-rod cover broke - looked just like yours - I sent the busted one off to Overwater by post and they sent a brand new one back within three working days. I'd give them another go.