The platformer tutorial has a good solution I've been using
On "A" key down
Set mirrored
Simulate Platform Left
On "D" key down
set not mirrored
simulate platform right
However, if you have separate Left and Right animations, you can replace the Mirrored function with a boolean if they are going left or not, and in your animations differentiate it there.
Platform Moving
Set animation running
Platform moving
if BOOLEAN
Set animation left running
if NOT BOOLEAN
Set animation right running
Could also add an "platform on ground" to the moving checks as well if you want to make sure.