ABS in the 92 GS-R's suck ass. Pull the fuses and gravity bleed the system and refresh it with some new DOT-3, 4, 5 brake fluid. If it is mostly stock just use DOT-3.

Here is some helpful information I pulled in less than 3 seconds on GOOGLE.

"QUESTION: All those DOT numbers on brake fluid bottles are confusing.

What do they mean? They sure are confusing, and it's partly because they were determined by a federal agency (what a surprise). Brake fluids are classified by the U.S. Department of Transportation (DOT) by temperature range and viscosity. Just about the only ones you'll find in motor cycle brake systems are DOT 3, DOT 4, DOT 5, and DOT 5.1. DOT 3 and DOT 4 are polyglycol-based and can be mixed with each other. DOT 5.1 is actually based on a different chemical, but since it can be mixed with DOT 3 and DOT 4 it's lumped in with them and all three are commonly referred to as polyglycols. DOT 5.1 is also lighter in viscosity-about half that of DOT 4- because it was designed for the rapid cycling time of ABS systems. Now here's where the confusion comes in: DOT 5 is a silicone based fluid. Regardless of the fact that it's wedged in between DOT 4 and DOT 5.1, it's chemically dissimilar to the polyglycols. It will not mix with polyglycols, and should never be added to a system filled with polyglycol fluid. There's an added bit of confusion for owners of some European bikes, whose master cylinder reservoir caps say "Recommended fluid 3, 5," leading owners to believe they can use DOT 3, 4 or 5. There are no silicone based fluids in common use in Europe, however. There, the "5" designation is for a polyglycol based fluid, which is what these bikes are designed to use."


I hope that helps some!

-Trevor