I am considering buying a 99 C4S that had a replacement engine from Porsche installed at 70k (car is now at 88k). Do the replacement engines from Porsche generally have the problems of the earlier engines corrected?

 

The replacment engines will have many of the upgrades but are still known to have some issues common to M96 engines. The later the replacment was done (year) the more upgrades it will have. In generaly replacment engines are considered to be a plus in early cars.

 

Where is the best source to buy a replacement engine(crate engine) and what is the cost?

 

Like Dharn said, the more recent it was done, the more upgrades it would have but it'll still have the IMS that isn't much different than the original. Maybe a stronger block and less prone to crack heads?
You can get reman engines from the dealer(Suncoast etc) for 9k-12k ish? I think it depends on inventory and clearance etc.
The other option would be a rebuild.

 

IMHO a 996 with a Engine Replaced it worth more $$$$ hence is a +

 

I spoke to SunCoast this week and for a remanufactured 996 engine they want $16K to $18K...that's steep.....my year 2000 996 is only worth $20K.

 

damn...16-18k?
Well, if your engine goes...it's either....a reman engine...find a used engine....or a rebuild...there seems to be a few people on here that have rebuilt their engine from a few different sources
either way these engines are not cheap if they go