After sitting for some time, when my 1989 C4 is started, the front brake fluid chamber drops about 2/3. The trouble light does not come on since the rear chamber stays full.I believe this is from the high pressure pump running. The warning lights go out after about 20 seconds and stay off. When I stop the car for a period of time, the fluid chamber refills. What is going on????

 

You should do the extended C4 bleed procedure. It sounds like there is air in the system that is getting compressed as the pump runs, taking up the fluid in the reservoir. It then leaks back over time as the car sits.

As you know, air can be compressed, and fluid can't, so that's where the volume is going. It's probably the "bomb" (the black sphere in the frunk) that needs a bleed. Adrian Streather's book has a detailed How-To...

 

Yeah sounds like it could be air in the "bomb" aka the accumulator. Not terribly hard to bleed but you do need to take special care when doing so.