Help! Transmission slipping recurrently
 

I have a 2003 C180 Kompressor and am experiencing transmission problems. After about an hour or two of running the car in traffic, the transmission slips into neutral. I have to turn the ignition off to get the car back to normal. At times it gets stuck in 3rd or 4th gear, until I turn the car off and turn it back on again. Unfortunately I do not have an official dealership Mercedes technician within driving distance. The local Mercedes mechanic I showed the car to cant seem to understand whether it is an issue with an electronic chip or the computer system or the hydraulic base of the transmission.

Now since this doesnt happen all the time (perhaps a couple of times a week), whenever I have had the local technician run the computer to check what the fault is there is no fault picked by the computer. In the speedometer panel, there is no malfunction display, so I am stumped as to what to do.

I've changed the gear oil a couple of times, and each time I do that, the car runs fine for about a month or two, and then, back to square one.

The hydraulic base of the transmission is almost half the price of what the car is worth in fair value in the market, so I'm not sure that is what I'd want to replace.

Any help would be much appreciated.

check for gear box leaks or change filter in gear box