Do not forget the rev counter signal comes off the alternator which is belt driven, so even a slightly worn belt will change the figures.
Plus as the pump is a Bosch unit, adjusting the throttle stop will increase max rpm at a standstill, but not whilst under load as the internal governor will...
Guy who replaced my TC told me al the local car dealers use it, most of the time they get him to put it in.
But even a new TC is a short term fix as the rest of the box is still worn, though mine is still okay 1 year later.
The oil for modern autos is very specific.
Lr 4 speeds take atf which is red, 6 speed take a different oil which is straw coloured, later 8 speed take a different oil again straw coloured, not sure what the latest stuff uses.
Mercs were atf, the amg models used a special auto oil, pretty pricey...
Did you say you were going to change it?
Oil is cheap, engines and gearboxes are not, keep it long enough and you will find out.
In the old days we called them bar stool mechanics, now they are on the web.
As a mechanic of 30 odd years, I can tell you hand on heart gearbox oil should stay clean for a very long time, what you have is black, black means things are breaking down or/and the oil has never been changed.
LR say gearbox oil is good for 110k, LR are full of sh**, ZF who make the box say...
For 6 or 7 years my D3 soldiered on with that additive, but i found as time went on it needed new gearbox oil and additive annually to keep it sweet, in the end refurbed t/c fitted, which totally transformed the way the car drove, tbh best 1.2k I have spent on a car in years.
So it does work...
Water injection elbow, only need to remove the small bolt on part to check, not the whole exhaust elbow.
Injector pump timing?
Cambelt last change?
Engine running at full temperature?
Partsforengines are decent prices for spares.
Keep us updated as my port one is doing much the same, and it is...
I think it is bit of a myth when they say an engine is addicted to ether. If it needs ether every day regardless of weather, then yes it is most likely totally worn out, and that is where the addict bit comes from.
Some older indirect diesel engines are just rubbish at cold weather cold starts...
Blue smoke on start up, normally worn valve guides or worn/missing valve guide seals.
Blue smoke when running, normally means it's had it!
Some nice thick cheap 20/50 might work well in such an old girl, avoid anything thin or with the word synthetic in the title.