As for the seal number in the parts page, I would go to your dealer with the model and serial number of the machine to make sure you get the correct parts for your unit.
What would cause the seal to leak?

By the sounds of this the unit has low operating hours on it. The coolant is probably the long life coolant and this coolant is very corrosive to aluminum. The longer this coolant sites the more acidic it becomes. I my self use the old green antifreeze as I find this much more suited for my needs I change the coolant after every year of ridding.
You may want to try and change the coolant out first with the green coolant, and give the unit a good run. You may find that your seep from the weep hole on the water pump may stop. This will only work if the unit has been sitting for a long time and the seals are dry and set in their static position with little flexibility left. May be able to free the seal up or soften them up enough to have some life left in them. This in not a fix it may just by you some time before you will have to change out the seals, and you may be able to prove this theory. Good Luck
