ABS on a '90 Prelude

I recently had an instance where, after a slight softening of the
brake pedal, the ABS light came on, and when I checked under the hood
there was brake fluid all over the exterior of the ABS reservoir. My
regular mechanic had replaced the brake master cylinder only a month
prior, and neither one of us felt the problem was due to
that....UNLESS there was a change of debris contaminating the ABS
brake lines, but I'm not aware that the regular and ABS share fluid as
such.

At any rate, I topped off the ABS reservoir, and the ABS light has not
come on again (except during typical system check at start up, and
then goes right off).

Mechanic spoke with a fellow tech who works heavily on Honda, and he
thought a solenoid int he ABS may be showing signs of failure. If so,
can this be repaired without a total ABS rebuild, and at what cost? My
mechanic was still looking into this. I did speak with a Honda
dealership and they said they would just rebuild the whole ABS system
for $1700.

TIA