Well, it was very difficult to see and confirm, but i was able to get a small peek inside the tube, and it is, in fact, lined with some sort of material. Maybe teflon, maybe some sort of rubber. But, it was solid, so i think i’ll be fine from a sealing standpoint. Just fyi. I put an oring on the bottom parts that go into the block so that whennit is shoved down and bolted, it will seal in addition to the rtv i put on. The top, as I said is very tight with an oring.