Exhaust fumes from breather?

[Tris.]

I recently had a problem with excessive oil covering my my exhaust pipe.
I've since stripped the tin ware etc, and found no obvious problems apart from leaking push rod tubes/ seals, and the cooling fan bolt was loose.

I've replaced the push rod tubes and seals, refitted and torqued everything up to spec, and cleaned all the externals of the engine.

On starting the engine up, my garage quickly filled with exhaust fumes, the air filter and breather pipe were not connected at this point.

I've driven the car around the block, and I've got oil on the exhaust again. There is evidence of oil leaking on the case between the two centre pushrods on the right hand side of the engine.

While having the car running, there's loads of exhaust fumes coming from the pipe from the breather to the bottom of the case, no signs of fumes from the actual exhaust, although you can feel the usual compression from the exhaust...

Any of you guys got any ideas?

~Tris.

[Editor]

It's possible to get oil into the fan housing. I've heard there's a drain hole in it at the bottom which can get blocked. If the fan bolt was loose, the oil thrower thread may not have been able to fling it back in. Does that sound possible? It's not an area I've had to play with.
Excessive gases from a breather pipe sounds like ring or bore wear.