Depending on the amount of water you may have another issue but yes the seal can leak enough to put significant amounts of water into the boat (> 5 gal/hr). Did this occur suddenly or did it appear over time? Leaks thru the shaft or rudder packing generally happen over time, sudden leaks generally lend to other probabilities such as damaged and loose hoses or fittings(best case) or engine damage (worst case).
As far as I know there is no published information from the boat manufacturer (Sanger) as to how much is too much water. Our rule of thumb in the shop is a few cups of water in the boat is OK at the end of the day but if you have gallons at the end of the day it is time to address the issue.
If you want to call me at the shop I can help you troubleshoot the problem but we are in the process of moving to a new location so we may not be immediately avaiable. Good Luck
408 451 9596 (old)
408 271 2628 (new)