I don't have the special tool either and have just carefully tapped around the seal to seat it' I do second @miktdish above re the seal, those brown ones fit easy enough but do not last in this situation and many have started to leak in a few thousand miles. The plastic seal protector you get...

Well at least others may benefit from your info.

Be careful not to contaminate running surface if you add sealer [ original seal had a sealer already on the outside] Locating seal in housing can be done by careful tapping around the seal if seal fitting tool not available. One chap on here made his own turned from wood, rather neat.

Voltage readings are not the be all and end all of how well an wire delivers power, if it can not supply sufficient amps things will not work. This goes for any other connection such as the spade connection on the starter. Poor connection, no starty. Easy to make up some wires to test a relay...

Plus one on the above regards Original seal. Not sure about the one in post above as see no guide. OEM seal that comes with a plastic guide to get it in place correctly, also OEM gasket for housing that has pre applied sealer on it. Fitting, The seal is a ptfe type and must be fitted dry, no...

If the bolt holes in the brackets for the panhard have worn over size that will also needs sorting or you are wasting your time just renewing bolts an bushes, had to sort the axle one on mine, rusted thin, worn oval.

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.