That oil looks pretty bad!
I watched the video (no sound on this pc), and it looks like you had to force it into gear, from my experience that is because the engine isn't running. If you did the same thing but push the machine forward it should shift easier, also with it running, the transmission is getting oiled, lack of oil = harder to shift as well.
One other thing I can think of is on the other side of the engine is a clutch adjustment, that might be off, but that is best to check once the engine is running. Last thing I can think of (worst case) is bent shift forks, but lets not go there right now lol.