You aren't the only one with these problems . Particularly with the Plastruct items . The shapes that I've bought are a dark grey color ( ABS ) and nothing seems to work . Plastruct sells "Plastic Weld" which is suppossed to bond ABS to Styrene to butyrate plastics . I've never bought it because I figured I didn't need another cement sitting around . maybe it is the answer . Lately I avoid buying anythng that isn't styrene .
As for the small styrene rod snapping when MEK is applied , it is very frustrating . I've started to use small dabs of super glue to locate the rod in position , then go back afterwards with the MEK to permanently bond it in place . This seems to solve the problem , maybe since the rod is already stressed and set in place before it is applied .
I hope this helps .