I am coming across the same sort of problems John.
My house was built in 1940, which at that time, they used lead and cast iron for plumbing and waste. The house was 'modernised' in the very late 70's, which replaced everything with some sort of plastic. It was just after that when I purchased the house.
It now seems that the old piping wasn't UV protected, so it has started to deteriorate, especially the sealed joints on the exposed soil pipes. The sealing rings have all 'popped' apart.
Now the problem. The old piping was all in imperial measurement, and it now seems that modern piping is all metric, so it is not just a matter of replacing one part, but the whole lot. Big bucks.
John