Well, technically not a spanner… a 5/32 allen key. Whilst installing the overdrive, I managed to drop the allen key used to tighten the 3 grub screws on the new coupling. It slid out of site down to the lowest part of the transfer box.

One solution would be to removed the sump plate and extract it from beneath… drain the oil, remove the sump, trash the gasket, clean off all the old sealant, wait 2 weeks for a new gaskets and refit…. all the while with EP90 dripping out of the bottomless gearbox.

Another solution would be to extract it from the top using a magnet on a length of fencing wire…. but pretty sure  that wouldn’t work as the fencing wire would not be rigid enough….Turns out there’s a proper tool out there and my TD5 Defender owner colleague kindly leant me his. (The tool, not the Defender)

From the left. Magnet on a spring, grapple on a spring and a spare magnet 
First, remove the filler plate from the aluminium transfer box
Second, what will the magnet actually lift. Lets try a 26mm combination spanner
Managed to lift the spanner onto its side. The allen key I’m after weighs next to nothing but I don’t want to spend the afternoon fishing about for it. Need something stronger.
The “car arial” at the top of the picture has a round neodymium magnet in the end. Coupled with the magnet on the end of the spring, it’s a lot stronger
Plenty strong enough
As this isn’t my tool, I covered the end and most of the spring in gaffer tape. This will stop the spring and blue plastic end piece filling with gear oil. It will also secure the magnet on the end. Theres a lot of steel gearing to wriggle through.
In we go
At the bottom go the box now. Passing the OD input shaft and lay gear wasn’t so bad but the magnet did stick extremely well when the touched.
First time. One 5/32 allen key removed. Reminds me of the children’s board game “Operation” 

Refit cover plate, remove gaffer tape, open beer… in that order 🙂