I am glad that the dealer got the straight story on no oil in that area. Unfortunately, removing the powerhead is the only way to fix it.
When you take it apart, be sure to follow the official Honda manual from helminc.com. Take your time and take a lot of pictures so you get the hoses etc put back into the right place and routed the correct way.
Also, be very careful in keeping the teeth of shift linkage under the powerhead aligned correctly. Although, it you get everything back on and it is out of alignment, the manual has a way to correct it without taking the powerhead back off.
Just a quick look at the seals that will be needed...they will be in the neighbor of $400 - $500. I am sure you will do a careful exam of the bottom of the block to check for any bad seals or core plugs. Also check the crank seal very carefully. I think you can change it without disassembling the engine...although I have not tried it myself yet.
When you make your stand, make sure there will be room to tilt the motor up for you can take off the lower unit and some of the lower parts of the engine. It is much easier on the back that way.\
Mike