We have an Evinrude 8HP outboard motor from 1996. It had been operating normally until yesterday, when the motor suddenly stopped responding to the throttle. When we opened it up, we found loose parts: a plastic assembly, a linkage, and a set screw.
According to a diagram we found online, the loose parts (red circle) seem to fit to some kind of post (green). There was an o-ring on the post that has started to deteriorate (blue).
We tried to reassemble the motor (first photo below), but the parts pop back off when we operate the throttle (second photo below). The post has a groove at the end, which we thought would be for the o-ring, but the diagram seems to imply that the o-ring should be inside the plastic part. The part pops off with the o-ring on either side of the plastic part.
Does anyone know enough about these type of motors to identify the issue? We are specifically unsure of which side the o-ring should go on, whether the partial breakage of the o-ring is enough to cause the failure, and whether there could be another part to secure it not featured in the diagram (e.g. a cotter pin)?