daddiojiggy,

The nipple should be solidly attached to the plate. Mine was loose as you describe yours to be. I called the Topsider folks and they sent me a new fitting with the nipple solidly crimped/sweged/whatever to the plate. It works well now. You might try sealing the nipple joint with RTV compound while you're waiting.

Regards,
Sixto
91 300SE
86 300SDL (due soon)
81 300SD (for sale cheap)