I've found on my older permanent stands that the tree, as it grows, will pull nails or screws right thru the wooden stand. I've had to re-nail the older ones several times as the tree "absorbs" the old nails.

At the very least, I would replace the lag bolts as they may be rusted or underconsiderable stress. If you find that the growing tree is actually pulling the screw thru the 4X4, I would replace that also.