kJelt, I had the same problem with my Dell U2412M except I made it worse by pressing the bug while it was walking around so the bug was now dead and permanently stuck between the LCD panel and the back light filter.
I'm working from memory here as it was a few months ago but this is how I fixed mine.
I basically stripped it down the way you did, being extra careful with the bezel and I also unscrewed the screws holding the switch PCB (It's a PITA to but it back as it has to be aligned well).
I took the iron surround off that holds the glass in.
With the help of another person, they held the monitor upright and tilted the top forward slightly until the LCD glass fell forward on an angle, the side of the glass with the ribbon remained where it was as a pivot point.
The side that needs to be tilted forward is the side that doesn't have the ribbon flex cable (I can't remember if this is the top or the bottom, so you may need to turn it upside down so that the ribbon flex is closest to your table and this becomes the picot point).
Be very careful with this ribbon flex cable as it is delicate as is the glass, it is very very thin.
Once the glass was forward, I could easily see the bug stuck on the back light filter.
There is not much room to get in there, the glass is leaning forward less than 45 degrees and the rest of the panel is perfectly upright, I then used a damp cotton tip to clean the bug off the back light filter.
I then used a dry cotton tip to get rid of the moisture.
I also noticed some dust particles located where I thought there were a couple of dead pixels for a long time.
I cleaned these dust particles off with compressed air in a can.
Do not touch the inside of the LCD glass to avoid finger prints.
Put the glass upright and put the whole LCD panel on it's back.
Align the glass to make sure it's located in the middle of the panel.
Carefully put the iron surround back on and re-assemble the rest of the monitor.
I had to play with the control switch PCB ass'y to get it to fit back on as the cable gets in the way and the screws are tiny.
Once back together, my panel was clean, no dead pixels (Caused by dust) and as a bonus, I could swear the back light bleed was less noticeable and more uniform.