When the o-rings are new, it's a b!tch to get the pipe on the first time. The first o-ring goes in OK, but the second one always wants to bulge out on one side. At least this is what I experienced with my SB-50JK.
You just need to work at it and be very careful to push the pipe on straight. Some oil on the pipe and o-rings helps, but the key is to push the pipe on straight. I also found that if it does bulge out, you can pull on the pipe while gently nudging the bulge back into the opening with a popsicle stick.
Once the o-rings get hot, they tend to harden and flatten a bit, so you won't experience this for subsequent installations unless you replace the o-rings.