Basically nothing. The valve cover gaskets started leaking oil on the exhaust, so I replaced them at a marginal cost.
The 912 is a quite underrated car. It benefits from the classic lines of the 911-series body, but is not hampered by the bulk of the six-cylindred engine. A standard ´69 912 is around 100 kgs lighter than a similar year 911. With 90 horses on tap from engine of the latest generation Porsche 356 for a 950 kg car it is not as slow as one might think. The sound from the twin-carbed 1600 ccm engine is actually enjoyable, especially with a louder exhaust.
I do a lot of track driving in various cars, and I've found, that the handling of the 912 is very good and predictable. If you push it too far in a corner it will just understeer gently. The mythical 911-oversteer will only occur if you use weight transfer (feint) before the corner. Even under heavy drifting it is easily controllable.
The non-servo all round disc brakes are very good with plenty of pedal feel. And speaking of pedals - those Porsche-engineers knew what they were doing, the pedals are correctly set up for heel and toe-driving.
But what sets it apart is the quality and feedback of the non servoed steering. If the tires are properly inflated the car will tell you exactly what you need to know. A great car!
Bet they weren't too fast with the 4 cylinder engine. Wasn't it the engine from the 356?
While it is true that the 90hp engine was not as powerful as the 120hp 6 cyl of the 911, the 912 had better balance. The same vintage 911 was heavy in the rear and a properly set up 912 is a VERY pleasant surprise in the twisties.
Don't get my wrong... The newer 911's would spank it all day long. But that does not take away one bit of the 912's charm.
Great little car.
I thought my '68 912 was a great handling car until went to the Skip Barber 3-Day School. After I got back from Roebling Road Raceway near Savannah, GA, I realized that I hadn't gotten half the performance out of it that was built in; it felt like the Crossle Formula Fords we used at the Barber school.
I could corner faster in one lane than I'd gone using two before. In other words, it helps to know how to drive the thing. I wish I could have fixed mine up when it got old. I now have a 944 which is amazing. But I still long to have another 912. Make that lust.