Should be right above the oil filter.
Water can not leak from the rear main seal, only oil. Most likely there is a leaking freeze plug near the rear main seal dripping water onto it.
The type of oil that should be used in a 2005 Jeep Liberty is 5W30. You can switch to 10W30 in the warmer months.
10w30
Enough for it to be full.
10w30
5w30
6 quarts with filter.
10w3010w30
4,828km
10w30
5w30