I own a 1996 E220 (Manual Transmission) (South African Spec) with the M111 engine. As of late I have been having intermittent problems with starting the car, both warm-start and cold-start.
Whe I turn the ignition to "On" position all dash-lights come on as per usual, but when I make the final turn to ignite the engine, nothing happens. Not a click, not even an attempt to turn over. It's as if the immobilisor is active (Aftermarket Vesa 4 system).

I initially replaced the actual starter as I thought the Solenoid was acting up. Following this replacement, at least two weeks went by without any issues, and then it started up again. I then proceded to replace the Ignition Barrel as it was worn. Again, following this replacement, no issues for a couple of weeks and then out of the blue, the problem started up again. Battery is also new.

The dash lights does not dim when I try to start the car, it is just that nothing happens at all. I can hear the Petrol Pump priming, and that's where it ends.

I have read up on some international forums where similar issues were discussed. Based on these forums it is possible that it could be the K38 Relay, but the issues are usually paired with other symptoms which is not present on my vehicle.

Can anyone relate to my problem, and if so, what action/replacement parts were needed to resolve the problem?
Any assistance will be greatly appreciated. I do not have an unlimited budget to do Trial-and-error repairs to get to the bottom of the situation, so any help will be greatly appreciated.

Just as an added bit of information, the engine wiring harness was replaced before I took ownership of the vehicle.

Thanking you in advance