have an engineer look at it. if you are interested in purchasing, and the engineer confirms that there is a problem, then why not consult with the vendor and have them put a claim through on their policy as a condition of the sale. Once the problem is rectified, that should be the end of it.
As regards 'subsidence' in the Douglas area, would the claim not be for 'burst pipes' rather than 'subsidence'? The policy excess is much smaller and there is no exclusion for burst pipes, but may be for subsidence. it is usually impossible to say whether the burst pipe caused the building to subside or the subsidence caused the pipes to burst.
In my own view, there is no subsidence in Ireland, and that all claims or the vast majority are dealt with under the 'burst pipes' peril.