...............How did we end up with two different fork designs, one being so much easier to drain and fill than the other?...........
From a design perspective, it looks like a breakdown in communication, possibly during a restructuring of corporate management.
example:
Hey Bob ! is that new fork specification ready ?
Ya Joe, the drawings for the basic springrate & dampening are done & on the fileserver, just a bit of cleanup & they are good to go out for fabrication !
Thanks Bob, I'll tell the New Boss ! Bob? Bob? (Bob just got laid-off)
Joe tells new Boss - Hey Boss ! those fork drawings are available on the LAN, but - I'm not sure where Bob went.
New Boss tells Joe - go meet him at the welfare office.
New Boss accomplishes much during his climb up the ladder ! cuts costs ! reduces design time ! gets product out the door ! receives big bonus !
forks go off to manufacturing without drain plugs, workers giggle. Buyers don't notice omission. Mechanics laugh & count their blessings.