I just finised a 8 by 16 Douglas Fir frame (pumphouse) for which the timbers were freshly milled when I cut the joinery. For end sealer, I used Baileys end sealer, www.baileys-online.com. It does it's job better than any other end sealer that I've seen used. I also used it inside all mortices.
I worked outdoors for this project and if I was in the sun cutting joints I could hear and see the checks developing but if I stayed in the shade then the timbers remained stable. When the frame was done I used hot linseed oil for coating the surfaces -- that worked well to control checking too. Now that the frame has been standing -- roofed but unenclosed, I am happy with the end sealer but need more coats of oil. Good luck.
Anthony