While working on my holding tank plumbing (not a pleasant job, but at least I found the leak) I had to remove the port side exhaust hose. I had noticed some weeping from it last season, so assuming I was going to replace it anyway, I cut it off because it didn't want to slide off the elbow. Now taking a closer look, it looks like the weep was from the elbow or the riser / elbow joint, running down to where the hose connects, and dripping from there into the bilge. So the question is, is there a source for replacing these Osco manifolds / risers / elbows? The right side looks fine (knock on wood!). Motor is a 350Q with closed cooling.
Posting a final follow-up to this discussion so that anyone in the same situation searching for info might find it. I was able to get the Barr 20-0039 risers to fit the Osco 7068 manifold by grinding a small relief on the manifold end cap flange for the top two riser mounting bolts.