Keith, there's a nitrogen-filled accumulator located under the pilot's seat that maintains hydraulic pressure on the gear doors so they don't droop. On my plane, the main gear doors would droop first. Same as you, if you switched on the master, they would close tight, but after a week or so, they would be drooping maybe 1/2-3/4". I do have the electric hydraulic pump.
So this was a slow droop, nothing like what you're seeing, but I would look at the accumulator for sure. IIRC, it takes 500PSI (+/- 50PSI) nitrogen when servicing. Its fairly easy to rebuild if its leaking, o-ring kits are available.
Did you ever get this problem fixed before? It appears to have been going on for a couple of years now:
http://www.337skymaster.com/messages...ead.php?t=4577