That is strange, I've never had a sebenza come stiff, they have always been smooth as glass right out of the box.
Just got a Large Ebony from onlyfineknives and it was smooth as silk, I too like to disassemble and reassemble with crk grease when I get them just to inspect and make sure the grease hasn't broken down from sitting around.
When you put the knife back together, put the handles back together first, making sure to fully tighten all the screws.
Next assemble the blade - pivot bushing - and washers, and then slide the assmebly into the handles.
Push in the pivot screw and fully tighten the pivot.
This method makes sure that you don't pinch a washer because the blade won't slide in if a washer is off.
There should NOT be any adjustment on the pivot, fully tightened is the only way because of the pivot bushing construction.
Good luck! And enjoy one of the best knives ever made!