How to terminate a cash offer due to foundation damage not seen?

[Joy Hagerty]

I found a house for sale by owner like the interior remodeling. overlooked the damage caused by the foundation issues existed. I made a low ball (i thought) cash offer. Location is good. But cracked driveway and garage floor needs immediate attention, cost 10k. I want to terminate the contract. Seller is ok but wants in writing. How should i best approach the termination letter? What kind of verbage should i use or avoid? We had a simple Fsbo contract i downloaded. . Gives permission to terminate the contract within 10 days under the earnest money clause. Thanks for saving my rear in advance. Ken