2.5hp leaks oil during storage

[Colliander]

Dear Sirs,
Since 7 years I store my 2.5 hp Yamaha the same correct way in my Dory while I row ***** (the engine is horizontal with the front or let's say the choke button down, which is one of the correct ways to store the engine). I never had the least leak of oil. Now suddenly oil leaks. It is coming from somewhere behind the carb it seems. I've cleaned the engine and had it run for an hour. No oil leakage.
The oil level is exactly on the small round shiny metal plate which one can check the oil with through the round small window.
Any ideas of why this starts happening? Is a gasket broken somewhere?
Kind regards
Alfred Colliander
colliander@crosslearning.ch

[boats.net]

The crankcase vent is behind carb but it's just a hose and shouldn't be leaking.

[Colliander]

Oil leaking

Dear Sir,

I decreased the amount of oil to minimum. Leaking still happens. The mechanic here tells me nothing can be done as these small Yamahas tend to start suddenly leaking one day...

What would you do to stop the oil from leaking during storage on board of my boat?

Kind regards

Alfred Colliander

[boats.net]

Might elevate engine end up a little when laying it on side.