Livvy1960

I have a 2004 320CLK that is new to me and purchased as a project with a known transmission slipping issue.
The car has done 260,000miles and runs as sweet as a nut
On a previous MOT the owner was advised the rear diff was leaking and had it changed, sometime after this the car started to go into limp mode where it would start in 3rd gear
The owner replaced the transmission and all was apparently good but after a period of time the limp mode problem has come back and having spent more money at the garage it was unable to be fixed and now I have it as a project / challenge

I have an iCarsoft Code Reader and get the following message - The Gear is implausible or the Transmission is slipping

When I clear all of the codes I can turn the car on, select drive and select 1st gear and the car drives perfect up my drive (10m) I can then select reverse and its perfect

Conversely when I select Drive the car will drive perfect and pulls away in first but then I have a problem with reverse but will finally get selected after going into P & D a couple of times and I also notice that after this I can no longer select 1st 2nd or 3rd

My thoughts are that this was electrical because of it driving perfect in 1st etc
I have checked the Through Adapter and have renewed the seals but all ok
I have checked the TCM and there are no signs of oil or water and inside appears perfect

Any help will be much appreciated - BTW my next step is to drain the transmission fluid to see what I can find - Water, Burning, Large bits of stuff etc

Thanks in advance