1997 Volkswagen Jetta transmission shifting to neutral when

I have a 1997 VW Jetta GL with automatic transmission. Recently, when the car is cold only, it keeps shifting to neutral (or slips out of gear) for a few seconds and then reengages. This does not happen when the car warms up. There are 180K miles on the car and I have had the transmission fluid changed at 100K. I was wondering whether draining and filling the fluid would solve this problem or would it make it worse? The people at VW service told me that this is a sign of the transmission failing and even a fluid change may not fix it completely. Are these symptoms a sign of transmission failure or low fluid level? What is this general consensus on this? What is your advice/impression? I'd like to get a few more years of out it. Thanks.