Dreaded limp mode

[Bezza3]

Hi all

I’m hoping to get some help with a problem. Following a glow plug light on the dash I have done some research on here, found similar problems, took the advice, got it scanned, replaced some parts, and now the problem is worse. So I’m calling on the experts to hopefully share their experience and point me in the right direction. I’ll try and keep it to the point

Audi a6 c7 2012 2.0 TDI

I experienced a glow plug light “fault” on the dash and car went into limp mode. Light was yellow, was able to turn car off and on to reset and clear at least temporarily. 
This became intermittent, and although I couldn’t “make” the car fault, it appears to happen more at a constant ideal speed - 

EG motorway driving/speed when at a constant with little demand on acceleration  

driving the car around town doesn’t seem to cause a problem, when a constant change or use of acceleration is required.
 

This seems to be the key factor, not necessarily the actual speed.   

 

Had the car scanned at an independent garage, produced the fault code 

P040300 exhaust gas recirculation circuit intermittent. 
 

took the plunge and replaced the EGR valve. 

within a day or 2 the car faulted again, same symptoms. However, whilst a day or 2 more passed while I took it back the garage I had a low coolant light come on. Thought this was odd but never the less a bad coincidence. Priority switched to sorting out a suspect water leak. This involved swopping a few suspect pipes/elbows/clips until happy the system was pressurised and holding. 
In the mean time the car has had cleaning agents and forced REGEN to try and combat the glow plug light and limp mode I was experiencing. Unfortunately as the days have passed I have again had a low coolant light warning. Upon inspection I have now found the water is contaminated with what appears quite a “gritty” substance. It doesn’t appear to be oil or another form of liquid mix. This seems alarming given the EGR valve has its own cooler…and now appears to be part of the bigger problem  

 

at this point i am drawing a blank! Iv attached the scan reading, in hope someone has experienced something similar.  
Thanks in advance 

VIN: WAUZZZ4G9CN173285
    Car: Audi A6
    Year: 2012
    Body type: Saloon
    Mileage: 124724 KM

---------------------------------------------------------------
01 Engine

    System description: R4 2.0l TDI
    Software number: 03L906018LA
    Software version: 9978
    Hardware number: 03L906018JL
    Hardware version: H24
    ODX name: EV_ECM20TDI01103L906018LA
    ODX version: 003012
    Long coding: 0A194012243401080000

    Trouble codes: 
        P040300 - Exhaust Gas Recirculation Circuit
            Intermittent
        P040300 - Exhaust Gas Recirculation Circuit
            Intermittent
                Date: 2022-11-18 10:22:39
                Mileage: 119343 km
                Priority: 2
                Malfunction frequency counter: 13
                Unlearning counter: 255
                Engine speed: 2038.50 1/min
                Normed load value: 62.0 %
                Vehicle speed: 110 km/h
                Coolant temperature: 70 °C
                Intake air temperature: 14 °C
                Ambient air pressure: 980 mbar
                Voltage terminal 30: 14.520 V
                Dynamic environmental data: 2096221026180E10C20BDF132F0F031331004011ED3700070411A9338B
        P012100 - Throttle/Pedal Pos.Sensor A Circ. Range/Performance
            Intermittent