You don't need OS3.9 to fix that.
http://aminet.net/package/util/sys/PatchRAM(The reason it happens is that the RAM Disk is dynamic, it grows and shrinks as needed, so every block allocated is in use and hence the RAM Disk has 0% free - it does not mean that your RAM is full. Look at the screen title bar to see how much free memory you actually have, or use a patch.)
