I do not understand what is going on as I do not have limp mode and no error codes at all. Car have almost 200000 km and gearbox was not working smooth after I was playing with shift selector. I decide change gearbox oil as is old and probably never service.

I give car to mechanic which is working only with gearbox and everything was good for 1 week. one day I try to start car and car was shutoff same time when engine start. i try again and car start and drive normally. Its happen again in week time and suddenly I couldn't start at all.
I call to mechanic and explain to him what my problem. He told me move to N and try again. I was surprised as this work. He told me sensor on conductor plate can be faulty. Mean time I did my own research on internet and found loot of different comments and post about leak from connector or oil inside TCU.
I check everything and yes TCU was full of oil. I cleaned and was no difference. After few attempt car start and I drove to workshop. We connect one of there scanner (not Star) and no code. They opened plug from gearbox and was oil inside not much just 10-15 drops. They cleaned and car start with out problem but i know if i wa driving car I need to wait at least 4-5h or next day to check if everything is good. Unfortunately this didn't fix the problem car didn't start from first time but did on second attempt. I thought yes I found problem as is better then before. I ordered conductor plate to change over. unfortunately After 5 days was back to normal i need ON and OFF car 5-10 times. What I found if I cant start car information from gearbox are not on cluster. When they popup I'm able to start car and car is driving not bad but not perfect. After car is start I can switch off/on/off/on/off/on and will start every time. I can go back to car after 1 and will work fine

Now question time
1. From computer cluster is getting information about status of gerbox. In my understanding all components like gearbox, snifter selector are connected to TCU but yesterday i found out if i can start car also computer is not showing how many KM I can drive on my reserve fuel. When everything is working is showing otherwise not.
2. Because I found oil inside TCU that means oil is still inside wire. Oil can damage harness ??
3. MB star 3 is able to find all those gremlins ??
4. Any Member from here is living in Melbourne and have MB Star scanner ??

What should I check first or change as this is far far away from my knowledge about this car, I owning W140 form 8 years and was few issues at beginning and no problems at all.

 

Sounds like you have a CAN problem. Have it properly diagnosed by a Benz specialist or dealer. Not worth guessing at at this point.

 

 

I thinking to buy MB Star 3 and try to do my self. Dealers will charge you $150 for start. I diagnose car with few tools and is no codes at all.

 

Even if Oil is in wiring system should be no issue as all Conductor plate is inside gearbox covered by same oil including Also solenoid and connection.
If it will be can-bus issue car wile be not start at all also I will experience issue while I'm driving.

All those symptoms are not making any sense to me. It need to be some explanation.
I can change TCU no problem but car is driving with out issue apart of start.
If will be wiring issue car will be having problem while driving but everything is working good.

 

You are assuming that the starting problem has to be related to the TCU or shifter or transmission. What if the brushes are worn and sticking in the starter? Or if the start relay contacts are burned?

 

Just because it runs, doesn't mean there's not a communication issue interrupting the "ok to start" signal that has to come from multiple modules at the same time. Once started, if the same modules drop off, it doesn't stop running.

Proper diag is key here. You can see the actual values of the related systems with DAS when it won't start, and figure out what's missing.