Two years since I last took out the heat exchanger core.
Majors dramas last time, it was corroded into the housing, it took a 20 ton press to remove it, also broken studs corroded into the housing and a bent/cracked end cap.
This time it came out with the gentlest of taps from a nylon hammer. Also removed and checked the mixing elbow, there was a small leak developing from the gasket. It has all been flushed, cleaned, inspected and put back together with new gaskets and orings. Confident with the the cooling system for another two years.