No problem. This has worked for me.
Firstly you will need to remove the hpfp. Once done, clamp firmly in a vice, taking care not to damage any bits on the pump.
Once clamped, remove these three torx screws. *take note - some fluid will leak out, so have a couple of rags handy.
IMPORTANT - if the fluid coming out of the pump stinks of fuel, one or more of the o-rings on the bellows have failed and will need to be replaced.
Once the pump is apart, clamp the pump like so:
Place a screwdriver in the slot below, and strike counter-clockwise with a hammer until the cam is loose
You should now be left with this:
Push the rotary seal (in red out, and discard)
The other end of the pump will look like this:
Give everything a good clean with some brake cleaner or similar.
Next, reassemble everything in reverse order - but don't install the cam gear or the new rotary seal yet.
Should look like this:
So next, you want to apply some vacuum to the diaphragm. I found some clear hose lying around which fit snuggly into the diaphragms hole, and just sucked on it a few times to create a strong vacuum on it. I then clamped the pipe to hold the vacuum while I refilled the pump. (a mighty vac or similar would probably do a better job, but I didn't have one to hand)
Next, find a suitable bolt that threads into the pump's shaft. Like so:
Once the bolt is installed, start filling the pump down the side of the shaft with CHF11S. (red arrow) Fill it until it is almost overflowing, and then with a drill or an impact, slowly start cycling the pump. You will notice the fluid start disappearing into the pump, and bubbles emerging. Repeat this several times (5-10x) until the pump no longer takes any fluid, and bubbles have stopped coming out.
Now, remove the bolt, and install your new rotary oil seal. (22mm X 11mm X 7mm) Take care installing this seal. It has no seat, and you don't want to push it in too far:
Next, thread that cam gear back in, no need to tighten, engine rotation will do that.
Remove your vacuum, and that's it. Job done. Re-install, and hopefully, rail pressure is back. You can and should remeasure the diaphragm before installation. It should be well below 20mm.
As an additional note. I have found, that on my pump, the pressure in the pump would eventually pop out the rotary seal. I have since had a machine shop cut a groove into the pump to take a circlip, which has solved this problem.
And that's it. Hope it helps.
**some of the pics in this post are not mine, as I didn't photograph every step.