problem sourcing and fitting plastic drainage pipes

I have an upstairs basin where the drainage pipe goes through the wall, through a couple of obtuse bends and into the soil pipe. It is all push fit connectors fitted years ago. The plastic connectors are leaking badly and water runs down my outside wall. The obtuse elbows are marked as 1 1/4 inches or 32mm but the plastic pipe does not seem to be 32mm as when I bought brand new obtuse elbows of 32mm the existing pipe won't fit. The actual plastic pipework is 31mm inside diameter and 36mm outside diameter. The soil stack the pipework connects to is marked 32mm and a 32mm pipe easily fits but the plastic cap with the rubber washer is broken.
Anyone know where I can get replacement obtuse elbows and a replacement fitting for the existing soil pipe inlet?
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