Did you ever solve your problem? If so, how?
I have a Kohler CH25 with the exact same symptoms, and like above, I mow on some fairly steep inclines. I did not have this problem when I was mowing on flat land before I moved. It is an issue because the oil contaminates the paper filter to the point I have to replace them frequently.
When I replaced a bad head gasket on one side (oil fouled plug), it solved a backfiring problem but not the oil on the carb platter problem. At that time, I opened up the breather and did not notice any defects, so reinstalled it, but perhaps i should just replace the reed and breather filter at this point.
Do I need to replace any other parts? I looked at a "kit" for the breather assembly but it didn't include the reed or filter; just the cover and gasket. Any other suggestions? Is it possible the other side has a bad head gasket letting pressure into the crankcase even though there is no oil fouling (both plugs look fine)?
I thought of two options if this doesn't work:
a. Purchasing a K & N air filter for this engine. Apparently, this filter is supposed to be oiled since it is not a paper filter. My thought is that at least it would not keep plugging up as fast, and when it did I could wash it.
b. Install an oil trap, similar to what one might use as a water trap on a compressor, routing a new tube from the breather to the trap and then back up to the carb.
I would REALLY like to know how to solve this problem. It doesn't burn oil; it just seems to blow it out the breather when I mow on my slopes. It is not overfilled.
Robert