I am off to look for the muffler. I have two refer compressors, this boat was really set up for cruising by a previous owner. The compressor for the port refer is under the settee cushion just forward of the sink galley, that one needed a recharge but now seems to be OK. The area under the galley sink seems to crowded to fit an compressor.
The starboard compressor for the refer (freezer just aft of the Nav table) , is on top of the hot water heater in that starboard cockpit locker. The compressor for that refer is dead and I dont plan to use it so I might just cut the freon lines and remove it altogether. That would provide access to the muffler, assuming as you say, that is where it is.
I do not see any check valve near the dripless stuffing box or log shaft. As I indicated, there is a reducer fitting, probably bronze, in that area, reducing the exhaust hose from the rise to something smaller, maybe from 2" to 1 1/2" or whatever, and that maybe because of the smaller hose size for the muffler. But that reducer does not look like a check valve, i.e. no pins or shafts visible from the outside, when I get the 2" hose off that reducer (to change out the riser), I will look up into the reducer to make sure it is just a reducer.
Another curious thing about the exhaust piping. On my previous boat with an A4, great pains were taken to have a rise in the exhaust piping BEFORE the mixing elbow, the so called "hot section" with lots of insulation on that pipe. That rise was to prevent cooling water from flowing back into the engine. And lots of warning to close the raw water intake in case the engine did not start quickly, to prevent flooding the engine with raw water, a common occurrence. On my E34, there is no rise in the exhaust plumbing before the mixing elbow, just a 1 1/4 nipple connecting the exhaust flange to the mixing elbow and not even any insulation on that nipple. The output of the rise is pointed downward so that helps but is this exhaust piping situation normal for Ericson??