This should not be a difficult part to make for an engineering company, its just a case of how many would need to be sold to make it worth while, and as has been said previously there is a kit available " at a price ".
I would have thought a piece of threaded ( outside ) angled pipe could be screwed into where the filler plug is located ( would look like a letter " j " with the bottom part fitted to the gearbox filler hole, the upper part pointed to the engine bay and routed for easy access. Then a typical autobox dip stick and cover could be modified for the top part of the outlet from the filler plug. It would then be a case of experimenting with existing levels to find out hot & cold levels on the new dipstick. If its anything like my XJS it would have to be checked with the engine running and hot after a 10 mile drive. Would obviously take some time to get it right but its not impossible.
There again you could buy the kit and see how they do it...............
I'm sure the guys on here have completed more difficult tasks than this,
Cheers,

ArtyH

 

It would be interesting to know the co-efficient of expansion for the ATF. In theory, you could fill it cold (but running), close up the plug then drain the excess through the cooling pipes.

Another point worth noting is that since they are hotter, the exhaust pipes should cool quicker than the transmission. So there might be some mileage in running the engine for a bit until the transmission gets around 40, letting it cool for a while and then running it again to do the actual fill. Possibly even cooling the exhaust pipes actively (wet towels or something)

 

OK, I just did this job and let me tell you, it wasn't that bad. Two comments though.

1) If you are just topping up, make sure to have the car running *before* removing the fill plug. Otherwise you'll have a quart or two of transmission fluid rapidly exiting the transmission. Fortunately, I happened to have a large piece of cardboard underneath and the edges were turned up in a way that caught all the oil.

2)Rev's video to the contrary, on my 2001, I found there was plenty of room to get the fill plug up and put in finger tight with my bare fingers without all the tools and without having my delicate flesh touching the hot exhaust. Once finger tight, I was able to tighten the plug with one of those L-shaped hex wrenches (though that setup Rev had would have worked fine also but you would probably have wanted to let the exhaust cool a little with that).

The remote temperature sensor was a good idea. I happened to have one lying around (an amazingly handy tool once you have one). I got fed up waiting for 40 so "went" at 38 though there was a 4C difference from one end of the transmission to the other so it probably averaged around 40. The fluid had stopped running out around 36 anyway and was down to a slow drip.

I think the car wasn't completely level. But if it's that critical, that's just crazy.