Thanks to all who replied! I'll check the pins and the "o-ring being left in" does not really apply as I am using all new parts.

But the locking ring is a good suggestion - but for screwing in the center 7mm screw, should the lock ring be in the fully locked or fully unlocked position?

Never mind, it's easy enough for me to try both - hopefully one will work.....

Thanks again - things were going so well except for a silly little screw that should have just run right in!
Larry