This may not work in your situation but I was able to repair my pump.
1. I removed the pump and disassembled it.
2. Went to this website and compared my pump components
to their diagram-photos.
3. I noticed a small ball-valve in the diagram that I didn't see in
pile of pump parts.
4. Upon closer inspection I discovered the ball wedged into the
barrel of the stainless or aluminum piston rod.
5. I replaced the ball as it looked worn. For lack of
anything better that was immediately available
I cut off a large round pinhead
found in my sewing kit.
6. After reassembly and re-installation of the pump I tried it out.
Nothing! Well I had to go somewhere and came back three
hours later and turned the machine on for one last try -
as of now it's working! Steam and espresso both on line.
Only one of the o-rings in the pump looked like it needed to be
replaced. Maybe some of the fine springs need to be replaced
as well. The machine is seven years old and I just saved $250
not replacing the it. And I saved $75.00 dollars not
buying a new pump.
I also took snapshots as I disassembled everything so
I'd remember what went where....good luck.