I've had this type of leak on my '90 Westy since I bought it 4 years ago.
The previous owner hardly ever drove it and when I first bought it leaked
a fair amount. I assumed I would be doing head gaskets soon. After driving
it daily and putting some miles on it the leak got much better! I had the
coolent changed, added about 1/3 of a tube of Alumisil and it's still
going strong. It leakes a little but I can go for a month without adding
any water.