I had exactly the same problem. Just went back to T-Mobile Netherlands, and they admitted directly that this is a common issue. They repaired it under warranty conditions at no fee at all. They just replaced the entire screen and luckily I've never faced the problem again.
Also, when the oilish liquid was there, the screen alignment was always a little outlined, and when you tap the slylus on that spot you can hear a strange hard "click".
T-Mobile G2 Touch [HTC Hero]
Kernel-versie: 2.6.27-0078c992 htc-kernel@and18-2 #821
Build-nummer: 184.108.40.206 CL#69351 release-keys