I know Volvo parts are expensive.
But you sure you want to put used parts in the cooling system?
You tried flushing or taking it to a radiator shop for an acid dip?
The link Raven posted is for a tested unit: it's tested for leaks not flow.
What's the motor doing that you think the exchanger needs to be replaced?
I've found the manifolds the biggest problem for the 125/131
Fill out the profile,location.
You might be close to someone who can help.