/castrandom has never worked for me. when i tried it the macro got stuck on my conscencrate on my palidan and wouldn't do anything until the CD was up so i went with my own castsequence so i had my skill when i needed it.

I dont know why you would want to random anything really. i use one button or LB one for chain lightning and this for lava burst

/castsequence [nomod] flameshock, lavaburst
/use [mod:shift] 13
/cast [mod:shift] elemental mastery
/cast [mod:shift] lava burst

i use the shift modifier in case i have to use another shock like earth or wind and i still need lava to crit for the kill
and i have the flame shock glyph that adds 6 secs and lava burst doesnt consume it