I have a 2011 Go Devil 23 SD with about 20 hours on it. I was running out this morning and (unknowingly) had fuel leaking out from just below the small white plastic fuel filter at the engine. The motor started running strangely, backfired once and then died when I let of the throttle. I looked things over, found the leak and tightened the hose clamp, re-primed the engine and fired it up and headed on my way.

When I got back to the the boat ramp I noticed what appeared to be oil leaking out from the starboard side belt housing vent ? I am pretty new to the whole mud motor thing and really have no idea what is causing this or whether it is safe to run the motor with this happening? Anybody here have any idea what might be happening?

Open the drain plug and see if you have water in the housing. Duckdon

I did, no no water and no oil came out of the drain plug...

No water... How is the oil level in the motor? Notice any loss of oil in the engine? I am guessing the shaft seal between the block and the belt housing is bad. I would suggest that you take it back to the dealer and have it checked out. With only 20 hours my guess is that it came defective from the Briggs factory. It should be covered under warrenty. Duckdon

It is definitely oil, the engine oil level has gone down a bit since I started noticing the leak. I guess there is some sort of drive shaft seal in there that must be leaking. Is this a common problem? How big of a job is the repair?

Take the inspection plates off of the rear of the belt housing and make dern sure it is oil in the belt housing. It is normal for black powdered rubber to come out of the vent hole.

I lost a bolt holding the rear plate on the engine (the actual engine not the belt housing). It was leaking oil so bad you would swear it was coming from everywhere. It could very well be the same thing, a bolt on the engine come loose and allowing the oil to come out.

So check the engine bolts and takes those plates off and hollar back at us with your findings.

These bolts

If those bolts are tight and you in fact discover oil in the belt housing then I would say the rear seal on the engine is phugged and you will need to replace it.

All of those bolts look to be fine. There is motor oil (not belt residue/water/other) coming out of this vent hole;

If you say there is no doubt about it being oil coming out of that vent hole then the only way it can get in there that I know of is the rear seal of the engine has failed and allowing oil into the housing. I don't see how it could get there any other way.

I would still pull that rear inspection plate and see what your working with inside before I did anything.

The red is the bolt that rattled out of mine. Is this a dirt and oil mixture circled by the blue?

I would have to agree with pintail I think it is coming from the rear cover on the engine. Fortunately mine was fixed with a bolt and the gasket was ok.

There is no other oil in a GDSD - except motor oil....

The lower pulley and U-Joints have a small amount of grease
inside them - but the outdrive is basically a hollow box....

You most likely have a bad case gasket or shaft seal on your
motor which is leaking motor oil - or a loose bolt as has been
suggested.... My Briggs case gasket began leaking at 100 hours
so I had GD replace it under the Briggs warranty... Sure a lawn
mower shop could do it but they likely would not be familiar
with re adjusting the belt....

Take it to GD !

It has to be one of the two. Now with it coming out of the vent in two or three streams I would bet money it is the shaft seal.

If the case gasket is the culprit, how would that oil find its way into the belt housing and out of the vent hole?

When My gasket was leaking I found oil everywhere even on the front of the engine cover.

Have you taken the rear cover off and looked yet? We will be guessing until you take that cover off and look.

I was not aware of any sort of safety mechanism protecting the engine from a low oil malfunction? Is there really such a shut off mechanism?

If that is the case, I can just keep some oil handy and top it off when it gets low. All the oil slinging around will help prevent corrosion