John Deere F735 oil leak

[Nexus92900]

So I wanted an John Deere mower, and one I could fiddle with a bit, but got more than I bargained for. My F735 got a Yanmar 2 cyl V-diesel, and I noticed that when it was running under heavy strain (long, wet grass), it dumped engine oil. After a quick inspection I found it had to come from the rocker cover. So I started my disassembling of the rocker cover, and sure enough, engine oil came pouring out. This was when I was over my head here, I have never taken an engine apart, and dont have the slightest clue where to go from here. I can see that there is a drainage hole in the rocker cover, and assume excess oil comes out here. Any ideas of where to go from here? I could pay an expert to fix it, but where is the fun in that? Bear in mind that english isnt my main language, and technical stuff aint my strongest side.

Thanx in advance

 

[Scrubcadet10]

Have you checked your oil level on the dipstick?

 

[Nexus92900]

Yes, I can clearly see that the level is going down after each run (I assume that I have been running the engine fora total of 60 minutes, and the oil-level has dropped approx 30%. And my green lawn has spots of blackness randomly spattered around)