Hello Rich,
I've taken my MX Sport out three times in the water, no issues with leakage.
Yesterday, was using both the MX Sport and White's pi with water 950 coil, seeing if any differences with drag when submerged. The 950 coil on the Pi is a little easier to swing, but it tends to constantly be adjusted on the front coil portion as it was always moving upward. Didn't have this issue with the MX Sport 10" DD, remained level and doesn't float.
Pros and cons with both coils, I like the center mount portion of the 10" coil, if it was thinner drag would be less but over all the coil is great for water. Little on the drag side but I believe that's due to the coil thickness.
Plus, boy my MX Sport operates great in mineralized fresh water. Prospecting mode is best, use lowest SAT possible.
I ran mine with SAT at 3 sometimes 4, sens at 6, VCO ON position and of course with Prospecting mode.
Paul