I noticed last season a clean area on the case which indicated a case seal leak.
This test proved it.
Sealing the intake ports
(bicycle tire inner tube material)
Sealing the exhaust ports
Motor - compressed air connected to the pulse line
Exhaust side
Notice the air bubbles / clean portion to the bottom left of the picture.
These are soap bubbles caused by a seal leak.
On the intake side a second leak was found - circled in green
The power take off seal looks good - no bubbles.
I'll not bother testing the magneto seal right now - both seals will be replaced anyway. They'll be tested after replacement.
Video
Air bubbles
click here
M1V, 990KB, 8 sec