I gave it an attempt and I managed to solder it! Doesnt help that the tip of my soldering iron is beyond corroded and barely keeps the temperature. I never do this stuff!
Sounds like you need to re tin the tip and you will get much better soldering results. a dirty tip makes it hard the the solder to flux and flux is what not only keeps the solder joint clean and to help it flow right but it also helps the solder to melt. dirty solder wont melt easy. and wont stick well either.
To retip your iron get it up to heat and then take a wet paper towel (or an old cotton rag will work to. fold up the towel a few times and wet it a tiny bit so it dont burn an squeezes the hot tip with the wet paper towel and try to wipe as much solder off as you can and dip the tip in some flux and try wiping it off a few more times. IF it still dont come clean and if its corroded like you said. take some sand paper to it then retin it. by dipping the end in some flux then take some fluxed solder and touch it to the end and wipe the excess off with the wet paper towel or rag. and you should end up with a nice silver colored coating of solder on the iron and you will get some nice clean and smooth easy solder joints. a clean well tinned iron makes a big difference. some times if soldering near plastic if you hit the plastic by acident it gets all in the tinning and makes it get real dirty and corroded pretty quick.
on closing the case if its just because the edges are now messed up and any bs broken off try cleaning up the edge some with a razor blade and some hot glue to stick it together if you happen to have any. Its good stuff for things you can want to take apart again some day and even for holding down wires and covering your solder joints with but can be peeled off if needed with out damaging any thing.