Sucks to have something that seems to be an overwhelming task happen right in the middle of the season.
It's really not that bad (comparedto a car), if you have the tools. I would say you could do it without pulling the crankshaft. Pull the pan and the #5 main cap, you should be able to roll in a new seal.
It is a 3-point mount? Disconnect the battery. Take pictures of your electrical terminals, so you remember how they go back, before you disconnect them. Only remove what is necessary to pull the engine. Leave the engine wire harness intact.
Remove the water line from the jet, or wherever it is most easily accessible. Leave all the other water lines connected to the engine.
Disconnect the fuel line, probably from the mechanical fuel pump, or wherever It is most easily accessible at the engine.
Assuming through-transom exhaust, disconnect the exhaust hoses from the logs.
Pull the clamp off the bellhousing at the pump bearing cap. Disconnect the motor mounts from the block.
Lift the engine slightly so you don't bind the drive line on the pump shaft. Check for anything else you might have missed disconnecting, you don't want to test the maximum tensile strength of said items.
The engine will need to be pushed about 2" forward to disengage the driveline from the pump shaft.
You will need to remove the bellhousing and flexplate after removing the engine from the boat, but I would change the seal with the engine otherwise fully dressed.
Drain the oil. Remove and clean the oil pan. Inspect it for cracks. Inspect the rear of the block and #5 main cap for cracks or other potential oil leaks.
Remove and clean the rear main cap. Use lint free rags or paper towels. Now is a good time to see how the rear bearing looks.
Remove the top of the seal by carefully rolling it around the crankshaft. Inspect the seal to determine cause of failure. Make sure that your leak is not from somewhere else.
When you roll in the new seal, I like to intentionally misalign the parting lines of the seal and main cap. Make sure that the lip of the seal is pointing in. Put a smear of oil on the seal, bearings, and crankshaft journal. Put a dab of RTV on the parting lines of the seal. Reinstall the cap and torque to speck.
ALWAYS WORK CAREFULLY SO YOU DON'T SCRATCH THE MAIN JOURNAL.
If you work ambitiously, you can finish it in a day.
I don't mean any disrespect, but any oil in the bilge should not be considered normal. An Exxon Valdez oil spill in your bilge contributes the bad reputation jet boaters have.
