Hi guys, huge update about this after all this time. Basically I'm still with the problem so far I have done the following:
1. Bought a set of second hand gauges(luckily found a set, new ones cost 400€). Gauge started working fine for a couple of months and then started acting up with an occasional appearance of true level. Occasionally hitting the dial used to make it work. Now the gauge is showing around 1-4% fuel as soon as I turn on the ignition.
2. Today I removed the fuel level sender unit (bloody pain in the ass with the screwable lock. Followed the guide around here to push the contacts until they make the sound. and put in place but issue still remains the same.
My suspects range from the following possibilities:
1. As already mentioned by someone in this topic, the fuel pump unit might have not been replaced.
2. Bad fuse is ruled out as clock and water temp work fine and fuel gauge needle shows activity but bad reading.
3. Might be possible that the connector went bonkers (cleaned contacts with small screwdriver and cloth).
4. Could be that something is shorting the fuel level gauge after a period of time.
I believe that the following steps should be ruled out as I doubt they would fix the issue:
1. Resetting the ECU via reset procedure.
2. Fuel rail doesn't make much sense everything works well.
Possible next steps
1. I'm quite reluctant to removing the instrument cluster just to check if connectivity is proper, if a connection is not properly made, then all clusters wouldn't be working.
2. I'll be searching for the sender sensor on its own as the pump work fine. From what I can deduce though, the unit is sold as a whole which might be a pain. I don't know the actual price for it but seems that when a pump is involved, it is usually expensive, and in this case I'm definitely shouldn't be purchasing a used one.. so I'm up for quite an expense.
Can't possibly think of anything else that might be the issue. Anyone of you guys who has managed to sort this issue out got an idea please?