Mine has one, and I also saw one in a 7000 I fixed... never understood the purpose of a heavy solution like that. Took some time to figure it out.
Anyway, the plastic part has grooves inside the side walls that
squeeze around the PCB on top of the transformer. It snaps in once it
has slided in place towards the front of the deck, there are no screws
or anything like that. To remove it, you need to spread the sides of the
cover at the front and pull it back at the same time so the snap-in
bumps (I'm lacking a word here) climb on the sides of the PCB... then it
just pulls out.
Unfortunately it is rather hefty plastic and takes a
little bit force, and there might have been a couple more of these erm.. snap-in bumps along the sides. Tell the owner to peek under the plastic, I seem to recall it was rather obvious once you know you need to slide it out towards the rear.
Not too easy to explain it seems 
And yes, there is no room to remove the tray pulley for belt replacement until this plastic part is out of the way...