My dear P.M.,
I write to thank you for your personal handwritten letter of March 20th. 
I quite understand-and am glad you took my suggestion in the spirit in which it was made. I was a little anxious about that.
The disability you mention was clear to me when I wrote you. But I thought I would put the suggestion up to you and let you deal with it-as I did not quite know what weight you would place on the turmoil that no doubt it would give rise to.
Many thanks for the kind things you say in your letter, which I am afraid are not quite deserved-as the job here has been an easy one.
With all good wishes, I am, Yours sincerely, R. G. CASEY