Brake Electric Antilock problems of the 2005 Buick Lesabre

3/17/2005 traveled to myrtle beach, SC mostly on I-95. On the way I experienced periods of rain. The first time I noticed a problem was during rain when another vehicle caused me apply my brakes in an emergency situation. When I applied foot pressure in the normal manner the brakes did not respond properly, instead of slowing down immediately, I discovered I needed to apply at least 2-3 times more pressure (if not more) to get the brakes to slow the vehicle. I encountered this problem for the remainder of the trip whenever I was in wet conditions. I did not experience on dry roads at any speed, and I was driving at speeds of up to 75 mph. 3/23/2005 returned to harrisburg, PA. Experienced rain from the south carolina/north carolina border all the way home (approximately 520 miles). The rain varied in intensity from a light drizzle to a down-pour. The brakes continued to not slow the car in the normal way (my top speeds varied from 55 to 75 mph). I continued to have to apply excessive foot pressure to slow the vehicle or even get it to respond. When I applied the brake the response was very similar to driving a car from the 40's or 50's equipped with brake shoes that has been driven through a large puddle of water and the brake shoes needed to be dried by applying the brake pedal to dry them before they would take hold again. At one point I thought the floor mat might be the culprit and interfering with the operation of the brake pedal, but the mat was nowhere near the brake pedal. I took the car to the dealer, but the day I was able to do this there wasn't any rain and the problem could not be duplicated. When we receive heavy rain again I will be going back to the dealer.