Oil pump leak

My thoughts would be:

1. Were the O-rings made of the correct material. i.e. resistant to oil?

2. Were the O-rings the correct size?

3. Are the pump housing faces flat?

4. Is the housing cracked somewhere?

5. Is something preventing the housing from being screwed all the way down? The screws may be to the correct torque but they may not have pulled the cover all the way down.

I wouldn't expect to have to put Loctite on the O-ring, it should not need it.

Probably not approved, But I have sealed many difficult leaks on engines using Permatex ultra gray sealant, which is pretty much the same as Yamabond from the Yamaha dealer.  My Jabiru fuel pump was leaking oil and the approved sealants all failed.  Ultra Gray has been holding for a long time now.

Hi 

Did he buy the "O" rings from a Rotax service center or just went out and got some he thought would work?

Never trust what a previous owner tells you!  I'd get in there and put new, proper O-rings on myself and see what happens. You say it will be the third time, but it sounds like it will actually be your first time.

I agree with Tyler...  Previous owner may truly believe the mechanic replaced the o-rings, but unless it's logged as such, I would not rely on his or her memory of what the mechanic may or may not have told them they did...  Even if they were replaced, it's pretty easy to "pinch" an o-ring during assembly, especially for someone who doesn't work on Rotax engines all the time.  

Ditto for Roger's comment:  a "looks about right" o-ring might not be the right material, diameter, heat range, etc. to work properly.  If you want it fixed, get the approved parts and do it yourself.  Better yet, have a qualified Rotax mechanic do it.  Rotax approved parts may not be cheap, but new Rotax engines are a LOT more expensive...