[SOLVED] help with holes/seams

you can try fixing it by closing the seams before you decimate in blender.
to close the seam the easiest way I've found to do it is to go into edit mode, then move the camera inside the body so it faces the side with the issue. Use the select key to highlight the two vertices that are closest together along the seam gap and hit alt+m and merge at center.

sometimes it can be hard to select the vertices that are closest because they overlap or are inside one another, to make this easier click the box that lets you view all vertices instead of just surface ones. it looks like this: