Well an update...I bought a new key for $300 and it did not solve my issue. I went back to the drawing board and tried to diagnose further. Took apart the dash and removed the EIS. Was contemplating sending it to a company in BC for diag/repair but decided against it. It sat on my desk for about 3 days and then I tried putting it back in...IT WORKED!!! First time and every time since I've put the key in, the system unlocks the steering and then authorizes the key to turn and start. Fires right up every time. Even my oldest key that went "bad" is now working with a new case but same guts even tho it did not work before I removed the EIS. Yes, yes I know by just removing the EIS, it will not fix itself or reset anything. It seems to coincidental. Now my question is wtf just happened??? I'm fixing other probs that aren't as important as this in the dash like the linkage arms for my AC stepper motor but won't get here till next week. So I have a week to keep poking around before I'm going to want to button this up and move forward. Just hate putting it all back together when I never actually found the prob to fix.
Took a meter to my ESL and found it was putting out the proper voltage at all the key positions. So now I have 3 keys that all work to start the car (also have the new 4 button so I can pop my trunk w/o a key!!) but no reasoning in why this was happening. Most MB techs will say 85-90% of the time, it is the ESL that is the prob. Not the EIS but they love changing both just to make you spend more money and really feel like an MB owner
Sending my EIS and all 3 keys to BC is about $225 including shipping. Buying an SDS from Craigslist is $600 and the icarsoft MBll scanner is $150. I'm leaning towards purchasing the SDS as it can do waaaay more shit. I joined MBWorld and have been getting a ton of help there but now hit a snag. Still waiting for more techy advice lol