The jack socket on my friends Gretsch Tim Armstrong came loose and it got lost inside. This is a real pain in the neck because there's no jackplate to unscrew to gain access, just a hole in the body and an F-hole not big enough to get more than one finger in. Which you can't reach anything with anyway unless you've got fingers like ET.
To rescue the jack socket I taped up the guitar to avoid scratching it then made a hook from some stainless lockwire and fished it out of the F-hole. This involved peering through the jackplate hole so I could see but in the end wasn't actually as fiddly as expected.
This might not have been too hard but that's not where the jack socket needs to end up. So I threaded some more lockwire in through the jack hole, put the internal washer on then threaded the wire through the jack and wrapped it round the contacts to hold it in place.
Pulling gently on this got the jack socket in the right hole easily. Then I threaded the external nut and washer down the wire and tightened it up. I used a little Loctite on the nut to try and stop this happening again. The wire then pulled out through the jack.
That wasn't explained very well was it.
Anyway, the end result is that the guitar is usable again and I got to noodle about on it for a while. I worry that I didn't manage to get the nut tight enough as it started turning, but then the Loctite should stop it rattling loose.