The Classic Machinery Network

I have come across a Komatsu pc 20 digger for sale. Owner says it weighs 3.2 tonnes. It has a yellow frame and undercarriage, white top and long reach boom on rubber tracks. It is around 20 years old Thought I could find further details on the net but seems there are several models with that basic designation. Does any one know exactly what this machine is? Secondly I found it is uncommon as a resale item ( There are many kubota, jcb etc on e bay) Is this problem? Thanks, Tim