Fret Dress/Level question Flea Bass

DrBob

So I've one of the Wudtone under tension fret leveller bars, a couple of Hosco fret crowning files and some Crimson guitars fret rubbers and armed with this, admittedly basic setup I've managed to do five or so guitars over the last year or so. and whilst the results won't be worrying Jonathan and the team at Feline anytime soon the guitars have definitely been massively improved in terms of playability, action height, fret buzz etc.
So. The latest project I've taken on is a Flea bass that's needed a once over for a mate. I think the bar may be a little short but using the same got the neck up to tension, level and then dressed the frets, recrowned them, polished them etc etc. 
It's definitely better except that I'm getting some buzz on the D & G strings from fret 9-13/14ish and it's doing my nut in.
Sighting down the edge of the neck from bridge to neck it looks like the neck might have a bit of an 'S' thing going on, as in slight underbow from nut going through flat and into a overbow which appears to peak around the 12th fret.
Weird thing is, If I try my fret rocker (sorry, forgot, got one of them too) it's saying there are no high spots there. Not totally sure what's going on but I can't get the action as low as my EBMM SUB Sterling (US one that has been refretted by Feline.....) ..
Looking at my SUB it looks like it's been dresses with a fall away from the octave up. Would that help ? And if so can I achieve that with the Wudtone beam as that seems to be all about uniform flatness rather than allowing fall away ?
Or am I fighting a fundamental flaw in the neck with the 'S' in the neck ?

Funkfingers

The fret rocker tool only compares three adjacent frets at a time. It might not detect a twist.

The FLEA Bass was a distinctly budget instrument, constructed from low cost materials and parts. The necks are not the most stable under string tension. I could bend them with alarming ease.

DrBob

Funkfingers said:

The fret rocker tool only compares three adjacent frets at a time. It might not detect a twist.

The FLEA Bass was a distinctly budget instrument, constructed from low cost materials and parts. The necks are not the most stable under string tension. I could bend them with alarming ease.

I did worry that might be the case

FelineGuitars

If we regretted the Sterling there will be both fallaway in the wood and on the frets  resulting in clean playability (I hope)

DrBob

FelineGuitars said:

If we regretted the Sterling there will be both fallaway in the wood and on the frets  resulting in clean playability (I hope)

The Sterling used to be in one of the candid workshop shots on your website Jonathan along with Tom and your Dan Erlewine neck tension jig.
And yes it plays wonderfully, that's part of the problem.... By comparison anything else is simply not up to scratch ! ;-)