Did a whole guide on another forum. Really limited info on these newer transmissions. Here's a link

https://www.glaowners.com/threads/2021-2023-gla250-4matic-transmission-pan-removal.30765/?post_id=224796&nested_view=1#post-224796

And for oil level check which can only be done with Xentry

https://www.glaowners.com/threads/2021-gla250-4matic-transmission-service-for-8g-guide.30766/?post_id=224809&nested_view=1#post-224809

 

Hmmm not ideal but at least it can be checked in XENTRY thought you must drain it to measure it manually.

 

No DEFINITELY not. So I tried measuring what I drained and added a 1/2 litre more, I was way off. First time I ran Xentry check, I got nothing coming out last step. I turned car off, added about 3/4 litre, ran test again. This time I got some runoff and before it got to a complete drip, I put overflow drain plug back in. I wouldn't trust just adding same amount as drained, you just don't know how much tranny had. Admittedly, after using the much better liquid moli, transmission was smoother, car sounded quieter.
another thing off topic. I was running the Mobil 1 esp2 0w20. I would hear a slight rattle when revving engine. Switched to Mobil esp 5w30, WOW, what a difference, motor much quieter. That 0w20 turns to water real quick, will never use it again

 

Guess the physical check is the only way or the most accurate way. Thanks for your reply.