Tension spring for 2-3 gear.

I'm guessing this a valve body part since you are not pulling the trans. Is this a Mercedes or aftermarket part? Numbers?

Everyone recommends replacing it. It's a 2$ item and saves a lot.
It will smooth the shifting from 2-3rd gear (since these are the most used)
It's a DIY and this is where you can find details
722.6 Pressure regulator spring replacement - Benzworld.org - Mercedes-Benz Discussion Forum

Shouldn't take more then an hour if that's the only procedure you do.
No need to pull the tranny. Just the pan

By the way. I purchased a couple of them. If anyone is interested PM me.
Should get them early next week. Will try to take as many photos when i work on mine