ikay

Might be worth contacting SBS in Manchester - https://sbsav.co.uk/shop/spare-parts/behringer/

There's a printable page with an 11" radius gauge here - http://guitarhack.com.au/hacking-files/printable radius gauge.pdf

Don't know how old yours is (or whether version I or II) but this thread from TB mentions that some early batches of RB IIs had defective solder joints which caused some problems - https://www.talkbass.com/threads/gallien-krueger-1001rb-owners-did-they-fix-it-plese-help.179487/ GK seem to be pretty good at fixing faulty amps so may be worth contacting them. Polar.uk.com handle GK repairs in the UK - https://polar.uk.com/returns-and-warranty-repairs

You could just detune by a semitone and use a capo on the first fret...

Bartolini, Nordstrand and many other brand pickups are available from BassDirect here - http://www.bassdirect.co.uk/bass_guitar_specialists/Pickups.html

Excellent!

Chromes usually have blue silks but maybe Revelation have them custom made by d'Addario

Could be Status Hotwire flats, they have black silks at both ends.

The damaged windings are probably quite near the surface so one other thing you could try (still fiddly) would be to unwind the top few layers of winding until you reach the last point where it's broken. Then connect this bare end to the corresponding output wire. You'd end up with a few windings less than before but probably not enough to make a significant difference to the tone or output. Might be worth a try before you go for the rewind, not a lot to lose!

You'd need to find and join the corresponding loose ends which would be very difficult to do. Sounds like a rewind to me...

Well looks like it's definitely metric and regular M3 is too small so the next option up is M3.5 as andyjr1515 says. Worth trying as there is a degree of tolerance with the screw diameter so it should fit. If you can find any that is!

Surely open circuit on a single coil would kill the whole pickup not just one string?

I have a Polytune clip as well which is also excellent.

Korg Pitchblack works well for me, big display, easy to use, handles low B no problem.

The Barts will work fine with the Glock. How about just taking out the Glock and rewiring as passive? The snap and bite of single coils are part of what makes a Jazz sound like a Jazz!

That's an unusual one! If the A string pole pieces are no longer magnetic then that would do it, but how that could happen is a bit of a mystery. Sounds like a replacement job to me. Or you could try and re-magnetize the dead poles with a rare earth magnet - https://forums.fender.com/viewtopic.php?f=6&t=100572

This Fender Japan JB-75 on Far East Guitars also has JB-72M in the neck pocket (see pic about halfway down) - http://fareastguitars.jp/fj_jb75-90_3ts_mij_s029/fj_jb75-90_3ts_page.html And this thread on TB mentions the same curiosity - https://www.talkbass.com/threads/fender-jb-mij-75-ri-a-b-serial-1985-86-but-stamped-as-late-90s-jazz-bass.657437/ Sounds like it's normal for a JB-75 and the odd JB-72 pocket stamp is just a mystery!

My old BB1100 used to do this as well. I think it's something to do with how they've wired the active/passive switch so that it also switches the battery in. There's probably a fix using a pull-down resistor (or somesuch technical gizmology) to suppress the pop but I used to just turn down the volume before switching.

If it's in 3/4 something's not quite right after the dotted minim/crotchet rest

See schematic below. These measurements were taken from my original '57 Precision (see pic). Spacing between ferrules is actually 20mm. I'm sure dimensions varied a bit on these early models but this should get you going.