Hi HouMenPao,
Your directions sound correct except I can't be totally sure that it's the first right turn after the tunnel. And after you turn right, you go straight up a hill, there is no second right turn to be made.
I was last in Gubeikou nearly 3 years ago and my memory is vague too. Fortunately, all the local people are so friendly. They will point you in the right direction if you are alone or have no guide.
Also, there is most likely more than one way to reach the Wall and the way I went wasn't necessarily the best way, although it was easy enough. The Wall is clearly visible from the road, so it's not too hard to find your way to it.
This September I am planning to go back to Gubekou. I will visit Wohusan (west side of town) and Panlongshan (east side of town). Then I will pay more attention and have more information.
You are also correct that the map has no indication of north. Sorry about that!
North is up on this particular map but it would be a lot better if it showed north, and in the future I will try to make sure maps show which way is north. Thank you for your suggestion.