w463 big oil leak from automatic transmision...

Hi all,

I have w463 SWB `94 G320 petrol with automatic gear box...
Like to go little offroading with it, did it every month this summer... :)
So, I had problem few weeks ago, that in forest I lost gear and speed, I push acceleration pedal and no speed, like in neutral - motor working, but no gear. I couldn`t even switch my automatic gear box from drive to neutral or parking, it was stuck. So I pull over on forest road, switch off it, put in parking, differential was in neutral jumped out. And automatic transmission gear box oil lamp was on. All was working and slowly drive near to my house.
When I try to add oil it was leaking from some small plasmas box near gear box:

I found it in MB catalog under 045 - transmission case, vacuum box, solenoid valve control pressure cable. How I understand it has something to do with acceleration pedal/kickdown...
My question is, is it broken or maybe something wrong with my gear box maybe, because all oil is coming out it, maybe pressure not right... I was trying to find it used from w124, but no luck. Seems to me I will need to buy new one, only question does it can be broken. My local dealer said it is not popular part to request... :) Or problem is somewhere else maybe? :)