I removed, cleaned and refitted it yesterday morning - it took a couple of hours total but I'm not in any hurry. The elbow was heavily encrusted inside and the feeder pipe from the heat exchanger was partially blocked and artificially extended by encrustation. However, I removed most of the crud (various pointy tools) and ran water through from the tap once finished. It is in very good condition for its age (2006 B37) and has been refitted. I checked and cleaned the back end of the heat exchanger as well. There was a light congregation of crud inside the cover but nothing to worry about. I also checked/probed the holes in the exchanger unit and they were all clean. After fitting new o-ring (alternate supplier to VP) all went back together ok although fitting the heat exchanger hose is a bit fiddly. Now hoping that I get no exhaust steam when putting my foot down next season
As you say, an annual maintenance job.