Okay...I have 2 copies of Castle of Deciet, and would like to sell one off on Ebay. But I'm scared, because both carts share the same issue.
I have to lift the left side of the cart in order for them to play at all. I only have a top-loader to play my games on, so I don't know if that could be the issue or not. When they are seated all the way in I only get a grey screen.

Do all of them share the same issue ? Or did I just win the lottery or something ?
Appreciate any help u can give, peace. 

Nothing... 
Thought maybe a cpl of you guys could pop yours into a top-loader and tell me if it's the same or somethin', but I guess not.
Oh well. lol

The spare has been sold on here now anyway.

I would have liked to help, but I don't own a top loader, just the regular old NES.

I gave it a try on my RetroDuo and didn't find the same issue as you, though.

It's been awhile since your post, but my Castle of Deceit played in the top-loader fine when I played it several months ago.  I didn't have to do anything weird to it.