I am hoping this is the issue, it says from ZF manual overevving when starting from stop which implies it could be slipping when moving off but be fine afterwards which is what I am experiencing, plus the valve chatter could be the noise I hear on downshifts.

http://forum.a8parts.co.uk/attachmen...1&d=1567607804

That's sort of positive then. Do you have access to the gearbox filling tool?

Nothing that cannot be DIY'd.

A bottle, hose and a bend piece of pipe. The idea is to use pressurised garden spray bottle with a bent piece of brake pipe attached, it's harder to get it lifted and level.

Fingers crossed that this is the problem! What a great result that would be after your fears that the box was toast.

Well have not done anything yet, I guess I just keep finding excuses to delay bad news just in case if it's not oil level. :ROFL: Also having 3 cars and never needing more than 2 at the same time reduces the urgency. I's been the same in the past with only 1 car out of action things move pretty slowly but if I am down to one fully working car things start happening a lot faster.:)

Looks like some 5HP24 boxes came with dipstick to check level and at least some could be retrofitted with it. I wonder if we could do it on A/S8

http://www.meurosport.com/5HP24_Dip_Stick.php

With me being lazy bugger and probably not able to get the car lifted and level on the drive for the proper level check I think I will just disconnect cooler line by the radiator and pump in 1-1.5l of ATF and see if it changes anything. If that helps then I can proceed to proper level check and possibly fluid/filter change.

I recall asking the designer ages ago about that and IIRC the answer was: only if you're in the USA and come to me to get it fitted as the prototype.

So I filled about 1.2-1.3l of oil in the box through radiator pipe but no improvement. :( If anything it's worse now, could be fault developing further or the new oil has introduced more lubricity so it's slipping easier. It's slipping in 4th as well now and it's less often that I can get all gears to work OK and when they work kind of OK it's only for a short time before they start slipping again, I think it was probably slipping in 4th before as well I just did not feel but now it's more pronounced. 5th still working fine. After some more research I found out that the default failsafe mode for the box is 4th but if there is a problem with forth it goes to 5th. And if it goes to 5th in failsafe it's usually issue with A clutch, either broken drum or no oil pressure.

Interesting fact on Audi oil container it says that if stored in sealed container it can be used for 3 years since date of manufacture, but when filled in box it's good for life :ROFL:

Sent e-mail to Planet Gears in Peterborough this morning an the chap called me back said he was sorry about delay in calling me back as he was travelling to their London branch today, going from the phone number he was calling from https://reengineeredtransmissions.co.uk/ He was not going to speculate what was wrong and how much it will cost to repair but as an example he gave me some prices.

1.Remove box, half rebuild, refit, new filter and oil about £900-950 +VAT.
2.With a full rebuild less valve body around £1400+VAT
3.If there is something wrong with valve body it's £150-350, he did not specify and I did not ask but I guess +VAT

I asked what's the difference between half and full rebuilt, he said half rebuild includes all soft parts, full rebuild includes all wear parts.

I did forgot to ask about torque converter but I guess that's not included.

Not sure about next step but I guess changing oil and filter will probably be waste of time and money although oil can be had pretty cheaply https://www.ebay.de/itm/20-Liter-Aut...item54742d0d55

This is sounding very similar to my fault a few years ago, where the car remained driveable, but kept slipping into limp mode under anything but light throttle, with an incorrect gear ratio code.

Turned out to be a broken pipe from the valve body to one of the clutch packs.
Gearbox specialist diagnosed it and it only cost A$350 or $450 or something to repair.

Wishful thinking perhaps, but you never know your luck. The fact that it keeps driving is something.