Can confirm now that the used Mercedes Benz part that I sourced was a direct BOLT IN !!! This EXACT MB part number seems to be used in vehicles with OM642 from 2005 to 2021 with 5, 7 & 9 spd auto transmissions. How absolutely clever of MB to do something as 'smart' as this !
Getting it out & back in whilst on jack stands & ramps in the garage, laying on your back had its challenges. Was actually not the nightmare I was perceiving it to be. used two trolley jacks that I welded a M16 nut into the top of the cup, then bolted on a bit of 45x90 timber. Put one under the transfer case cross member & the other under the trans pan. Was quite sturdy & no chance of having it fall off.
Only moved it back about 150mm just enough to gain access to the flex plate bolts. Simply unbolted the old one, bolted in the 'new' replacement
The replacement that I sourced was in 'as new' condition. The ring gear was absolutely un marked
The one that came out was WAY worse than I could ever have imagined. I think most of this damage was from the previous starter as it was not throwing out the pinion properly. Checked the condition of this newly replaced starter & it was hardly visible of any wear on the pinion gear ... thank goodness !!!
No wonder it wouldn't crank over ???
I did re-use the original flex plate bolts to bolt on the replacement one. It was hard enough sourcing the flex plate, could imagine the drama getting new bolts ?
So hopefully this information will help other people that require a new flex plate / ring gear for their WH Grand Cherokee with the OM642 engine !