Are they still using that check valve on the 98 models? If so, it's somewhere in the lines right before they go up to the hood. Usually that thing blows a leak somewhere and spits fluid back into the engine compartment/cowl area instead of delivering it out of the hood where it is supposed to. The usual fix is to replace the check valve (or just do away with it, which is the second best fix).

Spray the wipers for a while and then look under the hood at the rear of the compartment to see if there is fluid sprayed around or dripped on something.

The nozzles themselves get clogged, but when all four clog at the same time, it's usually either the pump that died, or the check valve. If the pump doesn't run, that would be another thing to look at.
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Chris Herbst, near Chicago.