When you say your MK10 hit 145 today, do you mean that the IP was previously lower? If you are checking it at significantly higher tank pressure, that could account for some of the increase. I would just make a note of it and when you rebuild, pull a shim out or use a taller seat. You might also consider a 90 duro o-ring for the HP piston; I usually use polyurethene, but EPDM or viton would be fine as well. You can also have a close look at the piston stem where it contacts the o-ring; if there's a glaze on it, you can break it up with very very fine sandpaper. I use micromesh; it starts at 1500 grit and goes all the way to 12000. Touching up the piston shaft with maybe 1800, 2400, 3200 will really remove that glaze and allow the piston to retain grease a little better under the o-ring. This cuts down on friction, which of course is higher at really high supply pressures.
MK25s with the composite piston and a new seat should lock up extremely well; every one I've seen has a faster lock up than any of my MK10s. My MK10s tend to creep a little bit with a brand new seat, wear into a good quick lock up after a few dives, and if they sit for a few months, maybe creep a few PSI until I dive with them again.
Regarding whether the creep is a problem considering you're breathing off the reg every few seconds, that is a fair question to ask, and some manufacturers seem to specify that a certain amount of slow creep is acceptable. To me, I don't want my regs to creep at all. I do think incremental creep can be an indication that something is not right and it's probably time to rebuild. It's amazing how small an imperfection in either the seat or piston edge can cause pretty serious creep.
