Just some tidbits.....There is no wiring harness issue on 92 cars. The issue was 93-95.
While my 92500SL is CIS, I believe that 500E (same motor on the surface) is LH. Not sure about the 400, but stands to reason.
With any of the V8 MBs from this vintage, unless there is a gigantic, glaring problem, assume a code for "symptom x" indicates that about 2 dozen individual components are potentially at fault.
Basic troubleshooting - no matter if it's a lawn mower or a 400e, start with the most basic things first - as has been said - fuel filter is a good start. If you're going to replace parts based on what the codes say, unless you're wanting to undertake a $5k exercise, smallest part first. General stuff to any car.
What's your love for this car? If the ETA is original, then yes, it's something that fails and you should get a reman from beckmann technologies. I think they run around $800-$1200
Just like there are no "cheap" MBs (oxymoron of the century), beware of any MB that is a gift
I was "given" an 83 300D that was supposedly "in fine running shape," my first MB, and after I'd spent double what it was worth I finally pawned it off to a WVO nut else during the early biodiesel craze.