Yep, early cars had a vent and an opening for the washer low warning. If you fill the bottle to the brim, the first 1/2 litre or more just pours out when you drive. The TSB was to close off the hole for the level switch, and it helps a bit.
I removed the bottle, and fitted a short length of 1/2" hose to the vent, effectively raising its height. This worked perfectly.
My '03 car doesn't suffer with the problem, so I thought the problem was fixed on facelift cars.
Chris