Help to diagnose misfire on chevy vectra

Hi everyone. Im here because I run out of ideas. Im going to be through in the explanation, symptoms and tests i did. So I thank you before hand for reading to the end.

Ok basics:

2008 Chevrolet Vectra (south american market equivalent to Opel /Vauhall Astra)
Engine: 4 cylinder 2.0L N/A 20SE Engine (almost the same as the legendary reliable Opel C20NE)
60K miles on dash, purchased used with 55k miles. Its my only car.

Main problem:

Misfire, as i have a broken catback (and wont fix it until i can solve this problem cause it makes a lot easier to hear the engine) you can clearly hear occasionally a miss, either cold or on regular temperature. Also if you accelerate the car and keep revs constant you can hear some pops. Also when idle you can see the engine ocasionally shaking a bit when hearing a pop on the exhaust. Its always present the problem. No matter cold or hot weather. Night or day. But its not in the point that the engine is working on 3 cyl, its pretty usable and you wont notice it without paying attention to the engine.

Here is what i know:

1- Car has no codes, no present, not stored. I have a scanner and checked for them.
2- Car has a very strong smell of fuel coming off the exhaust when started cold. Goes away after a few minutes. Particularly noticeable on morning starts.
3- Sparkplug on cyl 2 is full of a dark crust and looks dry. I assume carbon deposits. Other sparkplugs look brown and normal, same brand and model.
4- When cold started and in O2 loop. Car goes immediately to negative short trims like -7% / -9% sometimes reaching -12%. Long trims remain between -1 and 1. When car is warm, short trims are mostly between -3% and +3%.
5- Performed a cylinder power balance test. Nothing odd.
6- Performed a leak down test (I dont have a compression tester). All cylinders where between 5 % and 8% leakage.
7- 0 coolant consumption and coolant looks clean. Very very little oil consumption (and I think its due to a rebel leak on the valve cover)

EDIT: 8- I forgot. If for some reason the car stalls (bad clutch timing or any error on my end) It takes a bit of work of the starter motor to start it again. You need to crank it for maybe 10 seconds for it to start again. If you just wait 30 seconds after the stall, it starts faultlessly.

Testing I have done:

YES I KNOW, cyl 2 injector is leaking right? That was my obvious tought too. So… I dropped a bottle of injector cleaner on half a tank of gas, put new sparkplugs on 2 and 3. And switched injector on cyl 2 for injector on cyl 3. Ran a week the car and I expected to pull sparkplug 3 and it to be full of carbon. Well. It wasnt. Again sparkplug 2 was starting to get carbon deposits and sparkplug 3 was near mint.

So i thought sparkplug wires. Measured resistance on all of them. Near identical values. Longer ones were a bit more resistant. But for sake of trying i changed wire 2 with wire 3 (ofc changing also the connection on the coil pack). Still having misfires.

Pulled all wires one by one with engine running and using a probe light to look for spark. All 4 wires looked the same.

So now im here. I really dont like the idea of tearing apart an engine with 60k miles that looks untouched when it has less than 10% leakeage and is consistent across all cylinders. Also i would like to think that if it is a mechanical problem (burnt valve seat or worn piston rings) the problem wouldnt be totally random. (I ve driven before a car with a burnt valve seat and it was allways on 3 cylinders on idle and was rough as hell) and this is not the case now.

Please help :'(