The last Yoshi I repacked, the can came apart at the part you have circled in the last picture. It had the same button-head allen screws as what held the end-cap on. I do Distinctly remember it being an absolute Bitch to remove though (as in, there were 2 250+lb guys yanking on it and it wasn't doing much).
I'd suggest giving it a gooad soak in some penetrating lube (probably from the inside, so you can just get a puddle of it sitting down there and leave the can upright for a night or two). Then on the 'inside' (towards the bike, away from view), try tapping a chissel to see if you cna get any seperation. It MAY just be an interfearance fit that's been all sooted together from a few years of use.
Good luck