I have an ASUS for 2+ years that has not yet broken so have not taken it apart.

Back in my mfg. days hotmelt discharges around 350-400F. Work time around 3-5 seconds. 

I dunno what the MS contractor uses but this is in the ballpark.

The heat gun does not need to melt the whole hotmelt deposit just release from the backside of the display probably around 250F - hotter than boiling water.

I see others have posted where to buy stuff.

If you wanna get in trouble raid your Wife's sewing kit for prybars, thimbles to block the heat, and a consumer grade hot gun. The hotmelt won't be as hot or aggressive as industrial but might be good enough to stick the thing back together.

Finally, since the battery is a year old the run time capacity may start to drop. Since it's apart a new battery will restart the charge/discharge cycles.