I just went and checked and the line on my 38 is copper. I would estimate that it has been on there at least 40 years so I am guessing that it may be original. I wonder when it fails if coolant enters the oil. That would be pretty tough for the bearings.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!