RMS problems persist in the 996 models and in smaller amount on the 997. But they usually occur in cars which have missed service intervals or haven't been looked after well. Its like any car if they aren't treated well they break. RMS is a big issue in the 996, but generally the RMS is changed or checked at every service interval. It owuld not put me off buying one. The only reason I didnt buy a 996 C4S over the Zd was it was 3-5 years older and cost 5k more the Zd was a bargain. But I look back on it and wish I had. Next time but I will be looking at a 997.
The 991 is like the 996 was to its air cooled descendants, its the third iteration of 911 and built new from the ground up including the engines so hopefully the weaknesses of the older engines will have been resolved but like said its too early to tell.
In the big picture 1-3% of all 996 911s had catastrophic engine failure and even less in the 997. It is not worth worrying about and the more you know the better so you can have it looked at. Porsche seem to think that they have to take the whole engine out to look/replace the RMS but a lot of the Porsche specialists will do this without taking the engine out and it wont cost a lot. The seal itself is only a few quid.
The only problem with RMS is that it shows no signs of leaking, there will be no oil under the car, as it is contained but if it does it can leak into some pretty important areas which is why it causes catastrophic engine failure.
Most of the other problems were sorted in the second gen 996 which is years 2001+ so I would stay away from the early engines because they had more problems.
IMS can also be solved pretty easily if your car suffers from it with an upgraded baring. So again no worries there.
....one day :roll:
996 is in budget but dated now I prefer my Zed 