I just went through a whole thread about this. I had gone to the top of Marcy and could have sworn I found a micro cache at the peak(It was before I officially cached). After chatting with other cachers, there was never officially a cache placed there, nor is there expected one to be approved there because of the delicate nature of the vegetation at the top. The best we came up with was that if any were placed, they would have and won't get approval and what I had thought I came across was an unapproved cache. I think I took the same way you are, don't remember, but we left the Loj, went past Marcy Dam and up to the top. I don't recall seeing any official caches posted for that trail. There are a few in the Placid region. As mentioned Heart of Jo, Placid Waters, Sara-Placid-drive-in and away from the crowd. Good Luck and enjoy the hikes.