More interesting discovery on my plane. Did an exhaust system replacement due to an incompatibility issue driven by a failure of the fixture that fixes the cross connect to the left manifold. Replacement cross connect was incompatible with existing manifolds. Anyway, as we navigated this problem we discovered another interesting configuration question. Parts Manual Fig. 39 is the reference. The parts in question are labeled 19 and 19a in the diagram. The aircraft is equipped with 19a, which includes the Service Bulletin enhancements in a production configuration. This part is clearly a replacement for the original. It does not include part 19 since the Serial Numbers Affected column indicates these are an either/or based on S/N. The problem is my aircraft S/N is in the part 19 group. Attempts to find a reference for part 19 (2708583-101) to simply get a look at it have come up with nothing. Any advice?