The couple that I have removed from T400's have been a steel fitting for a flared hardline....does it still have the factory steel hardlines? The thread should turn counter clockwise to remove.
And if its not steel it could be brass, I don't think copper would have a suitable application here, but someone may have hacked it in there at some point...either the copper or brass should be easy to drill, you could use a grease covered drill bit, to catch the material for removal, just go slow and clean the bit often, if its even accessible by drill???