Mike,
I have no knowledge about the Hatsan, but you can order a 2x resealing kit for the Marauder, and it has the special tool so you don't wreck the orings on the valve, as it passes the gauge block. This can be ordered through Archer Airguns, and I highly recommend it.
As far as instructions are concerned, there's really nothing on paper, but there are numerous videos on U tube on its disassembly and service. I have one on my channel Field Target Tech, I tried to cover pretty much everything involved in a rebuild. I would recommend that you watch several, not just mine, before you get started. It's a straightforward gun to work on, it's not difficult.
Tom Holland
Field Target Tech