First, you mentioned above that the leak could be coming from the "clamp system" or "two bulkheads". By "two bulkheads", do you mean where the lid sits on top of the bottom portion? This would be right where the clamp holds them together.
If it is coming from there, I would double check the o-ring, and re-seat it. My filter has leaked from the intersection of the lid/base before, and I re-seated the o-ring, and it worked normal again.
If that doesn't work, the o-ring should probably be replaced (if that is where the leak is coming from). You would type your filter model number in a search engine, and that should bring you to a website that sells replacement parts. Just be advised that the o-rings can expensive for what your getting, because they aren't bought in bulk.
You shouldn't have to remove the DE to replace the o-ring. If this is the o-ring that is between the lid and bottom portion of the housing, just do what you would normally do when you put lube on the o-ring. That would probably be draining the filter. I don't have a DE filter, so if you are supposed to re-add DE when the filter is drained, hopefully someone else will chime in on this.
EDIT: BTW, it would be helpful if you could provide a picture of the filter when it leaks.