[lucittm]

coxy,
I don't think your question was answered. There are two types of Dilavar. The first was the Porsche factory solution to the lower head studs pulling the threads out of the engine crankcase in the magnesium engines. This problem also emerged as the compression and engine size increased in the aluminum-cased engines. These new metal studs were installed by the factory beginning in 1984. I think these were P/N 993-101-170-51, fully threaded Dilavar ($37.00). The upper studs were still steel, P/N 911-101-172-00 ($10.75) in all cars except the turbo which used all Dilavar studs.
There were corrosion problems with the initial Dilavar studs in some extreme circumstances and the factory reverted back to coated steel, P/N 10-0115-101 ($14.00) for all but the turbo cars. The second type of Dilavar studs were re-engineered for the turbo engines five years later, in 1989, P/N 993-101-170-53 ($43.00) and seem to hold up well.
In many engines, the studs have been replaced so you may have Dilavar studs in an early non-turbo car or steel studs in a turbo. I believe I have the 993TT studs in my car, they are reduced-diameter, coated black and a magnet will not stick to them.
Some people claim the Dilavar studs are too brittle and they break. There are just too many variables such as improper torque, abnormal engine stress, overheating, etc. to fault the metalurgy. Metal fatigue certainly plays a factor, but when the Porsche engineers found a strong metal (up to 170,000 psi) that expanded at about the same rate as all the aluminum in the flat six engine, I think that was a real accomplishment.
This information is based on the PP website and books I have read on the subject and not my personal experience, so don't hold me up to any of this.

Good Luck,
Mark