There is a mechanical lock that prevents the pull going back in until the key is turned to the on position. Perhaps because it came out to far [ location screw lost perhaps] the lock pawl is now in the way for the pull shaft to go back in. I think one of the pics in post you found shows the...

The cross bolt of the link plate may need tightening. Hook on link rod may need a tweek so it holds better. Side plates of lever may need a little squeeze to prevent rod hook escape. Button only rotates if hook has come out or its threads to rod have gone.

Key has to be in the on position for pull to go all the way in. [ or may just go in with screws removed ] one or tother.

ALLO ALLO, I will say this one more time. You are trying like many before you to get an old at least 40 years gauge along with its equally old wiring and regulator to be accurate. If it does happen it will be just pot luck and will not last as further deterioration naturally happens. Re my...

Getting door card off while shut is nigh impossible with out serious damage to it. Neither inner or outer handle will release I guess? Try holding up the lock button while working handle's. I button does not want to come up release it again. Now have a feel of the button on the door handle...

Cooling fan on alternator loose another check.

D box reverse idler got a bearing instead of a bush. Tidy idiot guide to the LT76 on LRUK forum. [ not saying you are an idiot, just what it is called.]

Intermittent is how mine was for a while so I had the under bonnet lash up and then the jumper until I sorted it. Some other relay behind the main group would click when testing mine [1990 19j] No glow plug relay on pre Defender model diesels just a heavy duty ignition switch unit. Can be...

Re my post above, when trying to sort my starting issue I made up a little jumper cable and plugged one end into the brown live feed [ at relay position] and touched the other end on the white/red to solenoid. Started every time. Connected small white from ignition switch through a test bulb to...

Send it back.

And the boost fail could be from something as simple as a pipe that has split or come off. Whooshing noise points to this, had it happen on a car once and power was gone.

Well, nice pics, could be anything but you have forgotten to tell us what vehicle year / type you have and what if any non standard extras fitted that may need the extra cable.

If air is getting in it has to be at the pump, any thing after would show as a leak.

To check for air coming through the system could you disconnect fuel pipe in the engine bay and run the pump with pipe in a clear jar to check.

As above, a problem selecting gears is a clutch, main box issue. Transfer box, put the diff lock in and see how much movement you have at the flanges [both props need to be off to do this properly] If there is a lot of slop when one flange is held and other turned it is likely a center diff issue.

The original ones still there? If so mark their position, cut off and weld replacements in the marked place.

As above @kermit_rr re thermostat. I often say for older vehicles you can not beat having an aftermarket capillary type temperature gauge, keep original for looks and fit it somewhere else. They read in numbers/degrees and no electrics to bother with other than light. Hope you pass on what you...

All series gauge's are getting well old. The one in mine just about lifts off the bottom when up to temp. Check what temp you actually have with a IR temp reader, aim at thermostat, top hose, rad bottom hose. I had a job to find a new thermostat for my Ninety last year, first replacement did...

Sorry to say but that is not a crack. That is the result of corrosion working out from the inside of the chassis box section. What is worse is that someone in the past has done a rubbish job of patching the area probably hiding worse underneath. What is the rest of chassis like? You cant beat...

No, not that I can see.