I have found that the Lynx City Bus system is the best to Sea World.
The day you want to go to Sea World, take a Disney Bus to Magic Kingdom, then take the monorail to TTC. Ask any Disney CM where the Lynx bus stop is.
Once you arrive, wait on Lynx #50.
When you board, you pay the driver $2 per person CASH EXACT CHANGE. Tell the driver you want to get off at Sea World. He will tell you the stop.
Then walk across the parking lot and you are there.
To depart, go back across the parking lot, then cross the street to the Lynx Bus Stop, then Board Lynx #50 to TTC.
The Lynx bus also stops at Downtown Disney, so if you want to stop there and take a bus back to your resort that is generally quicker. It is once again $2 per person CASH EXACT CHANGE.
FYI, If you want to get to Sea World early in the morning, the TTC is better because there is early transportation to the TTC. There is not early transportation to Downtown Disney.
Coming back in the evening, it is better to get off at Downtown Disney because there is late transportation to the resorts at Downtown Disney, there may not be late transportation to the resorts at Magic Kingdom.