This was purchased in the 1980s but probably has an older pub date. I remember a yellow cover with drawings. The family found a series of clues in their (new?) house and followed them to find a treasure. That’s all I remember! It might have been a new house or a summer house.
I read this book in the 90’s but do not know if it was published prior.
There is a young boy whom begrudgingly goes to a family members home (may be a grandparent although I do not recall this aspect specifically). I think it was for his summer vacation. There is a local legend of missing treasure, maybe it was stolen? Many people have looked for the treasure over the years, but of course the boy finds it in a barn. I think the barn was on the property where he had been staying for the summer.
The treasure had been melted down and molded/crafted into items commonly found in a barn and covered or painted to conceal it. I believe he chipped off some paint of a candle stick or something, and the wagon in the barn actually was made of gold and also painted or covered in disguise. I hope this is enough to figure this out, I really loved the book as a kid and now want to read it to my children.