Provided you are capable of making the statement contained in clause 4, I suggest leaving it there. If it's missing, the Court might come looking for further evidence.
That comes with the following caveats:
- If you weren't aware of the testator's capacity at the time he executed the will, you cannot make the statement;
- If have received any information which disputes he had the requisite capacity, you must disclose those circumstances;
- Bear in mind that a condition like 'progressive severe dementia' is most likely a bit of a slippery slope when it comes to capacity. Note whether the death certificate has a 'duration of last illness' noted, and compare that the time of execution of the will. Further note that just because it was diagnosed then doesn't mean that was when it started;
- Despite all that there is a presumption of capacity unless there is some evidence to rebut the presumption. If the will was prepared by a solicitor that may go some way to assisting the notion that he did have capacity, as solicitors are required to establish this to a reasonable level before allowing execution (but not definitively - that's up to the courts).