I tried cleaning my exhaust elbow with a recommended cleaner – Rydlime I think it was. The elbow fell apart inside as it seems the deposits were what was holding it together!
I replaced mine with a compatible part from Keypart https://www.keypart.com/stock/861906-r. They also have the Volvo part. It might be different for your engine though.
The membership association for owners of Dufour Yachts