Auch...

My car just stopped. The gearbox is malfunctioning. The roadside assistance did a readout of the computer and apparently it's stuck in 3rd gear.

The getrag 6dct450 is known as unreliable. I guess it needs full revision.

Even though the car only drove 148000km in 15 years.

Any tips? Any specific things I need to ask for?

I may be the only person who likes this transmission (2011, 200 000km, still Mr & Mrs Lucky)!

My points:

Is it otherwise in good condition with nothing else major on the horizon?
Has it had the proper oil and filter changes (AT LEAST every 3 yrs or 30 000 miles - if not that is a possible cause of troubles)?

Get a proper read of fault codes to see what is going on (Forscan)
Only DIY task (need to find and follow procedure exactly. It's not using the plug on the side as a level plug!) would be to change them both and see what happens (don't pay Ford prices)?
https://www.ebay.co.uk/itm/112436788478

Look for plastic particles in the filter and oil as this is the most likely cause of the problems (well, according to me) If that has caused the stuck solenoid or whatever, it will likely need a major repair?

That would cost maybe €100 to see if any improvement can be made at home otherwise you will need to sit down when getting any estimates?

Ask a "specialist" (but good ones are rare and any work should have a long guarantee and plenty of good references from customers, but still a risk)

That's all I can suggest....?

I only have this car since 2 months. I had it flushed. And that is probably the first flush it had at 150000km.

It didn't have any problems before this fault.

Tomorrow the car will go to a specialist who does a lot of these gearboxes. They will first do a diagnose of course. But probably revision. They rebuild with better quality parts.

 

Otherwise the car is in good condition (has already have a rebuilt engine and turbo).  So worth the investment.

If there's no service record on this gearbox, that is a definite Red Flag for problems.
On rare occasions a flush/oil change can stir up sediment that has previously been stuck  (I don't really believe this has happened!)

Hopefully the specialist can actually thoroughly diagnose (NOT JUST GUESS!) and check that there is no possibility of any external or electrical problems that are causing this issue i.e. they (you) need to be absolutely certain that it is an internal fault based on some solid fault codes and evidence (e.g. is there any evidence of plastic particles in the oil etc)

I wouldn't let them take it apart at great expense unless they can guarantee that work will produce a fix and you have a good warranty on any further issues, say at least a year (better 2 years!):

https://austrin-engineering.co.uk/services/#1488725417825-2758920e-e7efd3eb-d2400966-8526

Do come back and let us know the solution (I agree with your keeping the vehicle if at all possible - Good Luck but I don't rely on Luck!)

The car is fixed. Apparently it was clogged up. So revision needed.

I have to translate:

'complete revision.  replaced clutch plates for stronger type, replaced hydraulic brain, atf, cooler cleaned, calibration'

 

If it happened after the oil was changed then my doubt above was perhaps wrong, i.e. the flush may have stirred up more detritus (c__p)!

Were you told if it was "clogged up" (and was it solenoids  or other components) with plastic bits or say clutch plate residue, metallic residue on the sensors or something else (presumably all due to lack of oil change)?

Thanks

Clogged with clutch plate residue. No plastic bits.