To begin with, because MuseScore 3 does not yet support MDL, I am still using the most recent version of MuseScore 2.
I've had MDL installed for a while now--probably since it was released--and just recently, I discovered all sorts of SoundFonts to write with. Upon adding a soundfont, all instrument voicing is replaced by the most recent SoundFont. However, despite reordering my files in the Synthesizer, I cannot find any MDL drumline soundfonts--its as if they disappeared or weren't there to begin with. I also deleted and reinstalled MDL.