The DeLorean car uses DOT4 specification brake fluid for the brake AND clutch hydraulic systems. DOT4 is rated for a higher temperature than the more common DOT3 used in most modern cars. The temperature specification is probably not quite as critical for the clutch system, but it is convenient to use the same fluid in both systems. In an emergency DOT 3 may be used without harm, but it should be changed back to DOT4 when available.
All of our facilities use Castrol GT-LMA (now labeled as "synthetic" but Castrol insists that they have not changed the formula).
Conventional DOT3 and DOT4 fluids are hygroscopic, which means that any trace water introduced into the system will be absorbed into the fluid and minimize corrosion in the system. The DeLorean brake system is not water-tight at the reservoir (this is typical of most European cars, even to this day). Over time rain splash and atmospheric humidity will be introduced into the system. This is the reason for flushing the fluid every 2 years.
DeLorean Motor Company recommends against using DOT5 Silicone fluid. The usual reason given for using Silicone fluid is that, when it leaks, it will not damage painted surfaces. The trade-off is that silicone fluid is thicker and more prone to containing air bubbles, and is slightly more compressible in a system. This can cause a slight loss of pedal action (spongy pedal, which can be critical in getting full clutch release with the pedal on the floor. Silicone fluid is NOT hydroscopic, so any moisture in the system will remain in the form of "water bubbles" which is more corrosive to the internal metal parts. If using Silicone fluid, it still needs to be flushed periodically especially in cars stored out of doors or driven in wet weather.
Written 8/5/2016 DAS