Originally Posted by 97 SL320

That TCU is dated 98W53 , from all the other ones I've looked at, this would read 1998 / 53 rd week. 5WK33987 seems to be an internal Siemens number .

The F after 5WK33987 means it was flash programmed. This is typically found on replacement TCU units that are blank when made then programmed as needed. Given your car is an AMG, it is likely they programmed as needed due to low volumes. EGS51 is Electronic Gear Switching , type 51 ( or at least something close to that ) Later units were EGS52

What is the build date of your car?

The 135 error code is coming up "Intermittent fault: CAN engine management communication faulty". CAN ( Controller Area Network ) is a 2 wire communication system invented by Bosch in the mid 80's. The is how various modules communicate with each other. Pull up a tech paper on CAN as it is common across many auto brands and industry.

If the TCU was not talking to the engine computer, you would not get any shifts. I'm not sure how it would react to a momentary loss of communication.

A side note, the 2 wire system is redundant and is designed to work on one wire. The signals are differential , when one line is high , the other is low. This negates the effect of noise.

09/98 would be September 1998 , hardware version is just the revision level of the circuit board.