I called YS Parts and Service this morning and Rich advised that the problem was rare and that he had fixed those returned to him by using JB Weld (after roughening both surfaces). He felt that JB Weld would be stronger than the simple press fit used by the factory. Given the distance he suggested I do this myself rather than return to him because that's what he would do anyway. He also said that the problem had been caused in the past by the motor banging around and hitting the cowl or something.