Thought I'd update:

Sold diesel coupe.

Sourced and procured a 2.3l M102 from a 190E with low(ish) mileage to replace the defunct motor.

Decided this was the easiest and cheapest option for the time being, as I didn't really take to the N/A OM617, and therefore didn't want to waste effort swapping only to re-swap... I will drive the 230ce with the gas motor while I source a more ideal diesel powerplant.