Yamaha 25 outboard spent fuel leak

[robocop]

Hi everyone,I am hoping you might be able to put my fears to rest, that I might have a problem with my outboard engine.
I have a old Yamaha 25 two stroke outboard engine which has been serviced only last week, I noticed that it looked like I had some sort of leakage from the bottom bolt that secures the flange behind the prop to the casing, so I contacted my boat dealer who serviced the engine to find out what could have caused it and I was told it had been pressure tested ok and that it is a common problem with these older engines that the unspent fuel/oil seaps out of the lower bolt by the prop.
Not being wise on outboard engines I do not know if this could be true or not.
Could it be that the mixture had been to rich and would running for 5 minutes on a clean tank of petrol without the oil added to flush out any surplus mixture be of help.

I would be grateful of your thoughts please.
Regards
John

[rodbolt]

yes and ELLLLL NO.
your engine is running rich, thats whats causing the black goo to run down the exhaust.
all you have to do is figgure out why, compression,spark,fuel pump leak or carbs or the tstat is stuck or missing.