Thank you most heartily for——
How can I ever hope to repay you for——
I am extremely grateful to you for——
I am sending this letter as the silent messenger of my thanks and good wishes to you
I must find some way to make due acknowledgment of your goodness to me
I trust I may be able to do you some service, that I may be worthy of your kind approbation
I will not write more but wait until a better opportunity enables me to more fully express myself
Please allow me to send my most thankful acknowledgments for the favor you have conferred upon me
I know not how to express my grateful thanks for your——