Just finished cutting the silencer as I figured that it is defective anyway. Than I read your message. The description from you about the A26 silencer is about what I found. The silencer is burned through inside.
Making a new exhaust system is the only way now. It should not to be difficult because the old silencer was fitted about 80cm above waterline. (measures of the A31 are rather big).
For interest I added a few photographs of the cut open silencer.
Thank you for the advice it helps a lot to choose the proper parts.
Kind regards, Peter.