No sooner had I fixed the RH head gasket than .... gearbox fault....

I don't believe it's the battery,.... nanocom says "invalid throttle angle data", and then scrolling right says "engine torque fault.... On a short test drive i feel the box changing down as i brake (where before all was silky smooth), and it doesn't feel happy.
When I was doing the HG it was on a 10 degree slope (to my garage) for a couple of weeks. There's definitely D3 in it, need to wait until it has cooled to be sure of the level, but it was all v smooth before, and there's no reason to believe there's been a catastrophic leak while it has been stationary. The battery was disconnected during that time, I've put it on charge just in case.
And the sunroof spat out a rubber seal today too, but i'll deal with that another time...

btw - have reset adaptive values on nano, following the HG rebuild. Also, nano is not able to clear the gear box fault, even at position 2 on the ignition ie engine off.

Have a carefull look at the connectors, particularly to the TPS. It isn't unknown for moisture to get under the insulation and start to rot through the conductors. As you will have had them all unplugged, you may have strained one and broken it. I've had to carve away the plastic and solder the wire directly to the end of the terminal on my temp sender and intake air temp sender for just this reason. Once soldered, I've slobbered the ends with RTV to keep the moisture out.

yep, makes sense - seems like wiring or a sensor. The closed throttle position is giving 0.625 v, which I understand is in range. It's annoying as I suppose it is just one little fix away. Anyway, I'm away for a week, so guess I will take the trusty Defender.

0.62V is what mine shows so it's about spot on (or mine is wrong too), although that doesn't correlate with your throttle angle data being wrong. Unless it is staying at 0.6V and not going up as you open the throttle.

v odd. The wiring to the TPS looks in fairly decent nick, tbh. Rave seems to confirm that dodgy TPS signals will mess with the gearbox and gear changes, so it does seem to be something along these lines. I've disconnected the battery again. How long will it be before the P38 forgets it had a gearbox fault ie stops flagging it before I can even start the engine? (Nanocom won't let me delete it). I was just hoping if it was a bogus error it might go away after cutting off the power :o)

I don't know if it will ever forget, it doesn't seem to forget anything else. My throttle butterfly was intermittently sticking so it would idle at around 1,000 rpm and that made the downshifts very noticeable so I suspect yours is doing something similar. If it flags the error before you even start the engine that would suggest a wiring problem somewhere. May be nothing more than a connection you've had off needing a squirt of contact cleaner. Just a case of working out which one.....

yes, could be worse. I whipped off the TPS itself just now and sprayed that up, made no difference.

Just got back to base after taking the Defender to Dorset, and popped the bonnet on the P38 to spray up the connection from the engine loom to the gearbox at the rear LH of the engine by the transmission dipstick (since I was getting multiple errors ie both throttle and torque seemed like an obvious place to go). Once i'd done that and plugged it back in then the gearbox fault still registered, but the difference this time was that the Nano cleared the errors... Can't be sure the connector was properly clipped up in the first place (doh !! ). Problem solved. Tnx for your help GD

As it was the RH head you had off I assumed you hadn't touched the connector behind the LH head. That one is often forgotten about but it's pretty damned important.