I've got 300 hours on my O-235-C1 in the past two years and I am still chasing down oil seepage issues. None of them have been serious, more of an annoyance and a cleanliness issue.

I thought I would document some of my issues and resolutions.

First off, my engine had 6 hours since OH when I bought it, but it had been sitting (pickled) for 4 years. 

The very first leaks were concerning to me. It seemed some of the bottom case half bolts were seeping oil. At the same time I was getting some black stains between the cylinder barrel and the cylinder head. These continued for the first 50 hours or so and then stopped on their own. I made no attempt to tighten the case bolts having been warned about the potential problems with doing so. No idea why the case bolts would stop seeping, but they did.

I had heard that it is not unusual for new cylinders to seep some dark fluid between the cylinder barrel and head as some type of lubricant is typically used as part of the assembly process. This too stopped after a while. 

Then my oil pressure relief valve starting seeping, so I removed it, pulled out two washers to slightly lower my oil pressure (which it did) and installed a new copper crush washer. End of that leak. 

I was having repeated seepage with the rocker cover gaskets (cork). Replaced them with the silicone ones - and still had leaks. Since the rocker covers have standard screw heads I could not properly torque them. Recently I discovered (yes, a little late in the game...) that there is such a thing as a torque screwdriver. I spent the hundred dollars and properly torqued the rocker covers - end of leaks. 

This also taught me an important lesson - I DO NOT have torque calibrated hands!

I also bought a small 1/4" drive torque wrench and started going over a number of bolts/nuts, like the magnetos. I was WAY off on pretty much everything (too loose). I have since made a promise to myself to use a calibrated torque tool on everything I can when it comes to the engine. Yep, I know, this is probably something that is hammered into A&P training on the first day.... at least I finally figured it out..  

(To be clear here - I was using my 3/8" torque wrench on larger, critical components - spark plugs, propeller, starter and alternator mounting bolts, etc.. I just wast doing it on some of the small stuff - and any screws. Also there were some bolts/nuts that I could not get to with the 3/8" torque wrench that I can now get to with the much smaller 1/4" drive torque wrench.)

I installed an oil filter adapter and of course that leaked the first time (bolts not torqued properly).

The oil dipstick tube was not properly safety-wired and it came loose and started leaking.

One of the oil return lines from the cylinder head got loose and started seeping oil. Tightening that up fixed it.

I have had repeated leaks from the 3" oil return hose pieces that are on the oil return lines to the engine. I finally got tired of tightening the old thumbscrew type clamps and the small worm drive clamps. So today I pulled the oil return lines, removed the old hose pieces (on two of them the rubber was cracked at the ends) and replaced the hoses and worm drive clamps. Then I torqued them properly. Hopefully this will fix this leaky problem.

I hoping I won't have too many more leaks to deal with.

On one had this has been good for me. Since I was always concerned about leaks I have gotten in the habit of pulling the cowl every 10 to 15 hours just for a look. Spending so much time inspecting and fixing small things has gotten me very familiar with the engine and accessories.

The real lesson learned is the importance of torquing everything I can properly, whether it a nut, bolt or screw - and no matter the size. Everything has a published torque rating and not tightening to specs can end up wasting a bunch of my time.

I have also learned to keep my engine clean. I use various techniques to remove oil and stains everywhere I can and whenever they occur. By keeping all the components as clean as possible it helps identify new leaks/seepage. Of course it doesn't always help you locate the leaks. The pressure in the cowl has a way of blowing the oil everywhere, making it very difficult to trace many leaks to their source.

That's my leaky story...