Leak in the oil storage

[BuffUpdate]

Greetings everyone. After giving the area around the engine a thorough cleaning, I discovered that an oil leak is actually coming from a rectangular plastic cap located on the side of the engine, sandwiched between the sump and the bottom cover of the gearbox.
The oil cooler seals were replaced a couple of years ago on this 2011 E350.
Much obliged.

[BuffUpdate]

🫣

[Lemmand]

If the torque converter is located underneath, remove the cover to check for a leak in the back crankshaft seal.

The gearbox is being serviced.

[BuffUpdate]

That's exactly what I was considering after spending the afternoon poring over diagrams. I kind of miss the oil cooler days.

[Kenjibb]

If it's a small leak, I'd just watch it and fix it before the MOT.

[Kenjibb]

Consider giving this some try?

[Kenjibb]

https://www.ebay.co.uk/itm/405322479391?_skw=at+205+reseal&itmmeta=01KJZMRJVKQFTS20D273XVMKDF&hash=item5e5f1a371f:g:XOEAAeSwYfpo0pVa&itmprp=enc:AQALAAAAwGfYFPkwiKCW4ZNSs2u11xD02bGOr5hsT4hFbnecjxsuvWAT6uQ8rSkyXEtiIzf3O94HukkVooDBztM+kHGNxO95vgOWysgxoSyg+iQJgwH8X8GjdpCtr4OyrNNwWpzEs8iELh5fryy1YRRfmBH380c26v+46qZh9s7/kP7MeuXXp4qy+p6u54z86dRfxHXEoY22zBp53V7H+3xaHbVZbZGYJzEz5u9SC24TH9LZRMMnOOEdVR8tBQdodOgTgBHSEA==|tkp:BlBMUJKu4vSXZw&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338181125&toolid=10001&customid=2518X1570512X769054ddd16ea86c372270863ede4828&subId2=15

[RacingNight]

Used something similar on a BMW engine and it got the job done. Renewing it is necessary with each oil change.
It's not cheap to reseal ATP.