Cheers Bob. that's very kind of you.
However [fingers and toes crossed], I may have managed to contrapt something together that, in the finest traditions of long shots, 'might just work!'
Pull up a chair and some popcorn as we continue 'The Adventures of a Toyota Land Cruiser Rendered Undriveable by a 50p Part"...
As I said before, I hunted high and low round the house, trying to find something --Anything!-- with a likely looking diameter and thread pitch. A task made all the more difficult by the fact that the old plug is so fecked that it's barely got any threads left to compare to [which is why I'd find it difficult to supply you with the necessary spec,
@BobMurphy ]...
Hoping that, if I did find something that fitted, I could either cut it down to size or, if that wasn't feasible, at least have 'something' with the correct diameter and thread pitch to trundle off to B&Q with. In the end, I assembled this motley collection. [Yes, that thing with the wooden handle is off an old drill! You never know!]...
Off out for a sojourn under the motor, while I tried inserting these various objects into its orifice [Ooh, er, Missus!].
I found that none of them would go in cleanly. Some wouldn't start at all and others would do a half turn or so and then stop turning any further, without resorting to a spanner and a bit of effort. So I surmised that the threads inside the sump itself are probably lightly mangled too. Either that or Toyota have contrived to use some unbelievably obscure thread pitch, all their very own.
Before resorting to further spanner inflicted violence, I thought I'd have one last trawl around the house, on the off-chance. So, back to the ranch and I came across this. An old Battery Isolation Switch, which I'd bought to fit to a camper I was building years ago and never got round to. Thank the lord for my dearly held, girlfriend-annoying principle of 'Don't Throw That Out. It Might Come In Handy!'...
The terminals on that were also a likely looking size. So, after the switch had bravely sacrificed its life for the greater good...
I was left with two of these...
As you can see, comparing with what little is left of the original sump plug, it looks pretty close...
One slight problem though. You know that old saying about 'Square Pegs and Round Holes'. This wasn't likely to make a very good seal round the drain hole...
Still, I'm nothing if not resourceful [or is it 'too stupid to know better'? I can never tell the difference]. So I went back down to the truck again and tried my new candidate.
As with some of them before, it went in about half a turn and then stopped. But I reckoned, being made of copper, this particular bolt would be more easily persuaded to mould itself to whatever shape the threads in the sump were in, without actually causing any more damage to the sump itself.
There was still the problem of making a good seal though. So I threaded a nut and crush washer onto the bolt and then carefully tightened it into place with about as much penetration into the sump as the original would have had. [I could probably have wound it all the way in as there's quite a bit of clearance above the plug. But I didn't want to tempt fate and have it shear off and leave me with an even bigger problem. So I erred on the side of caution.
I then squeezed some red silicone in around the nut and washer and cinched them up tight. I'm hoping that the combination of the crush washer and the silicone will make a good enough seal to stop any leaks. I'll have to leave the silicone to cure overnight and then I'll chuck a bit of ATF in tomorrow and see what happens. I'm slightly disheartened that ATF [with Acetone] is one of the ingredients of DIY penetrating oil. So I reckon, if there is the slightest possibility for it to find a way down through the threads, it'll seize it with gusto.
But, anyway, here you have stuzbot's newly patented 'Double Adjustment Transmission Sump Plug'...
Keep your fingers crossed for me folks!
Incidentally. Trivia fans will be interested to know that, when I got under the wagon today, there was still ATF dripping out of the sump, albeit at a rate of one drip every few seconds. So I reckon I must have had the full 5 litres out by now. And it makes me wonder whether, if you left it long enough [months?] you could actually completely drain the thing. My big yoghurt carton I left underneath to catch the last stray drips was about half full when I checked during the week. So that's about anothe half litre accumulated, just in slow dripping.