TBH, I doubt he will remember the location after all this time, especially if he has mental issues.

Maybe not, but an indication off photographs would be a start.

They took Hindley up onto the moors (a couple of times ?) with photographs but were unable to pinpoint the exact locations - the photography experts on here will tell you but I imagine that if you are trying to judge how far away you are from a distant feature then your error of margin could be several hundred yards, even if you've got the correct straight line - you're then searching a peat moor which varies in depth and may even have shifted over the years (including its contents) and you're looking for bits of bones by prodding with spikes or using cadaver dogs, or even using ground radar - its a tall order.

They took Brady up shortly after Pauline Reade's body was found, but he couldn't pinpoint anything either. I don't think he could pinpoint it, even if he really wanted to with the shifts on the moor.

I doubt they'll ever find it until some unfortunate soul drives past his bones on the motorway or a dog finds them when fetching a stick.