Welcome Angrywood,
I'm guessing you used a factory style replacement switch(?)
This link says that's how they are supposed to work and also how to modify it to have the parklamps stay on.
This second link is for a rebuild kit for the master cylinder/clutch unit which should take of any leaking issues.
http://6066gmcguy.com/parklamp6063.html
http://www.rockauto.com/en/catalog/g...epair+kit,1840