Help required, new member!

I have quite a high powered YB cosworth engine in my Dax Rush and have engine oil (very small) on the bottom of my gear box, right where the gear box meets the engine, is this likely to be the half moon or the rear main seal on the engine? Unfortunately on the Dax you have to remove the whole engine to do the rear main seal so I want to be sure. Like I said it's engine oil on the bottom of the gear box, I was just wondering if it was a half moon would it leak through the gear box sandwich plate causing it to drip from the gear box?

 

Worst picture ever but that the oil at the bottom on the box (top of picture is gear box with oil, bottom of picture is my sump).

 

The mods will merge this thread to the other one. Try to stick to one post / thread.

 

might be rear crank seal or the sump gasket set up i cant remember if if they got half moons on the back been a while since i done mine the crank seals a fair old size just do both while its out. dip a cable tie into the g/box filler plug make sure its atf thats red if not it could be from the box