I drove my 912  approximately 11,000 miles, over a four year period, when the engine then developed a bad oil leak.  I determined that this leak was occurring somewhere under the fan shroud.  I used the  internet Porsche lists for advice and the consensus was that the leak could be either a bad oil cooler, a oil cooler seal failure, or worst case was the case could be cracked.  There was no way to know for sure without pulling the engine out of the car.  Once the engine was out it was obvious that the oil cooler was ok.  The oil residue seemed to be coming from under the base of the oil cooler.  I removed the oil cooler and inspected the base for any cracks.  I used a magnifying glass and was unable to detect any cracks in the case.  I then reasoned that the oil seals had failed and decided to put in new ones. The engine and tranni went back in the car.  Once the engine started, it took about 2 minutes for the bad news to occur.  The oil leak was even worse than before.  I called Harry Pellow for some advice.  He suggested that I remove the engine again and start it up on my garage floor without the fan shroud installed.  He said, that was the only way to see exactly where the oil leak was coming from.  He was right.  I set up the engine to start on my garage floor without the fan shroud.  I immediately saw where the leak was coming from.  It was seeping out of the case just to the side of the oil cooler.  I was depressed, but not for long.  I called Walt Watson at Competition Engineering and he said that they could heli-arc repair my case to better that new.  This was an opportunity to make my engine better...

Here are photos of the broken old oil cooler base and of the repaired case.  The area in the circle shows where the repair was done.  It was machined perfectly. I was very impressed!

 

Now since the engine had to be completely disassembled for the case to be repaired I decided to change a few things.  I went with the Norris 337s camshaft,  Shasta designed pistons and AC cylinders.

I also had my case modified for full flow oil filtering.  More to come on this 2nd rebuild....