Issue with the gearbox of the Mercedes W211 E270

[Paqngo]

Greetings to all, I require guidance concerning the gearbox of my E270 CDI. Herein lies a comprehensive account of the problem along with supplementary information that may prove beneficial.

Vehicle Identification Number: WDB2110161A309273

The issue at hand:

When the transmission is cold, the 1–2 shift can occasionally be quite abrupt and occurs rather early, approximately at 1600–1700 RPM.

Nevertheless, upon the gearbox reaching temperatures of approximately 80–90°C, I encounter a distinct issue between the 2nd and 3rd gears. As the vehicle nears 2000 RPM, the RPM begins to surge autonomously, suggesting a potential loss of hydraulic pressure or slippage in the gearbox, even in the absence of further throttle application. The RPM experiences a minor increase and oscillates for approximately 2–3 seconds before the gear ultimately engages.

It appears that the gearbox is unable to maintain pressure or execute a seamless 2–3 shift until it "engages" and finalises the transition.

The ATF was substituted 500 kilometres prior, along with a new filter and connector plug.

My inquiries:

Should I disassemble the gearbox to examine the valve body or clutch packs, or would it be more prudent to seek a quality pre-owned 722.640 unit?
What transmissions are compatible with my vehicle?
Is my vehicle exclusively compatible with the 722.640 gearbox from the 2.7 CDI?
Are transmissions from alternative engines (2.2 CDI, 3.2 CDI, petrol engines) compatible?
If they are physically compatible, are they also compatible in terms of electronics and hydraulics?

Any guidance or insights would be immensely valued.
I appreciate your assistance beforehand!

[dave783]

When did the issues commence? Should the ATF change occur prior to or subsequent to this? What is a reliable and esteemed oil brand utilised? Is the oil level verified twice? Is the TCU and connector plug devoid of oil?

[Paqngo]

The gearbox exhibited this problem prior to the fluid replacement.
I utilised authentic Mercedes ATF and fitted a completely new genuine Mercedes connector plug.
The antiquated plug contained gearbox fluid.
Furthermore, the gearbox pan utilised bolts that differed from the original equipment manufacturer, and the drain bolt was stripped — evidently, an unskilled individual had previously serviced the gearbox prior to my acquisition of the vehicle.
I have possessed the vehicle for approximately one year.

[Paqngo]

The ATF level is accurate and has been verified.
The technician who performed the most recent examination of the vehicle informed me that there is certainly an issue with the valve body, and it is highly probable that the clutch packs are also exhibiting wear.
This remains a hypothesis, as the vehicle has yet to undergo real-time data diagnostics; however, based on the observed symptoms, numerous individuals have indicated that fixing this gearbox might not be financially viable.

[Paqngo]

Numerous friction material residues were present at the base of the pan; however, the mechanic who replaced my ATF and filter noted that the interior of the gearbox appeared fairly pristine.