using soldering irons for this mod, i've found that different shaped tips play a big roll in the succes of the mod.  pointed types don't work well at all, the heat is only applied to a small point and the reflow underneath the acetate ribbon isn't satisfactory.

chisel tips have worked really great for me however

I've tried a hair dryer before and didn't get very effective results, but a hot air rework station is definitely the way to go if you happen to have one.

I was given a busted DMG which I've managed to repair, but the LCD has one dead horizontal line… I don't think there's been a successful repair of one to date, but I'm keen to experiment with hot air and see if I can work that out.

Yep. I got the lines on my DMG back with a hair dryer. I stopped applying air when I saw the LCD beginning turning black, wait a few seconds until it gets its normal color and apply hot air again, testing every time I stopped that I didn't f*ck up the screen. It's kinda easy, indeed.

OK, I just wanted to throw a bit of info out there.  This concerns the method of repairing the missing lines on the Gameboy screen, which I'm sure most of you know very well.  In my experience, I have found that the soldering iron trick does NOT work all the time.  After doing that on a few DMG-01s, only 1 got fixed & stayed fixed.  The others would not stay fixed at all.

However, I recently came back to one & tried my hot air rework station with a small nozzle & low pressure.  Hot air fixed the lines very easily, & they stayed fixed, even when I press on the cable.  What the soldering iron couldn't do, hot air did much better, & much easier too.  It seems that hot air works much better than a soldering iron.  I used around 300degC.  Of course, not everyone has a hot air rework station... you could use a heat gun, or even a hair dryer to heat the ribbon where the lines need to be fixed.  If anything, maybe block the air from blowing on the LCD itself too much.

Anyway, I recommend using hot air instead of a soldering iron to fix the lines.