If suggestions of cleaning the front ABS senders (sensor and pulse wheel) and associated electrical connectors doesn't stop the intermittent ABS activity then you may need new sensors. I found the original old style sensors (rectangular tipped) on my '89 700 were over-sensitive, especially at low speeds on very smooth surfaces. Your 1990 700 may or may not have come with the newer less sensitive style sensors (diamond shaped tip) or else received an in-warranty upgrade. If not, it would be a relatively easy DIY upgrade.

If you deide to replace the senders you could save a chunk of change getting these off a wreck. However, they are sometimes difficult to remove without breaking them especially if you twist too hard. Clean the area thoroughly, use penetrating oil (a day in advance if possible) and tap the back lightly a few thousand times to help break the bond.
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Dave -not to be confused with a real expert, just goofing around at this