Here is what I recommend. MDKEEHN13, go buy a quality new battery and let's eliminate that right way. Most go with the Diehard AGM Platinum for this car that is known to eat batteries. When you buy that also buy a quick disconnect you can attach to the (-) terminal so it is a quick turn of the top and you can disconnect. Do not leave it connected other than for testing. Buy a cheap multimeter on Amazon for less than $20 and watch a youtube video on how to use it before you touch those prongs to anything or stick them in anything (there are 100's of videos posted). Then we can get started looking for the power drain with that Multimeter giving you a base parasitic (or whatever one wants to call it) drain/draw when the the car is off... If it is higher than say 100 milliamps (which is high as perfect should be around 60 lets say). Then you start pulling fuses throughout and replacing one by one looking for the one or ones that drop the draw considerably. This is going to take a lot of time and this is just the start of fixing this mess. Your other options are to have it towed to an independent shop that specializes in European cars (preferably vintage Mercedes) and open your checkbook or list it for sale cheap and someone else with the time will take this project on. I really hope rodents didn't take up residence and chew on wiring throughout as that would be an absolute mess to figure out and I'd guess you do not have the free time to go down that road.