Attachment 433452
Your model does use the center trunnion locking handle, part "9" in the diagram. This is for locking the bevel position but, could help with stability when at 90 degrees as well. Is it tight when you are making your cut? I see that part(s) "7" have three bolts each. The extreme front and rear hold the bracket snug while the four 'corners' are loosened for blade alignment. Your alignment is good so I would not loosen these but, I would make sure that they are tight and that those castings are not cracked. It would be great to just find something that had worked loose instead of something that has broken as many parts for these saws are no longer available.