Upon further review, I'm pretty sure my double problem was a result of a sticky trigger bar. I had the 10320 striker in the pistol and I swapped it out for the 10300 and could still force a double on the bench, not every time, but maybe 1 of 10 times, similar to when the 320 was in the pistol. More parts cleaner and air to get the trigger bar to move completely up and back and I think it is fixed. I thought maybe one of the trigger bar springs had broken or somehow come loose or something like that, but, no, I think I got just enough of that heavy grease on the trigger bar to gum it up.
I am going to chalk this one up to gun owner error, as in, I used way too heavy of a grease in a firearm that only needs a drop of oil. I don't think any of the aftermarket parts are of concern here at all. I'll probably put the 320 striker back in the gun for range use only, but leave the 300 in place for carry. That is the way it should be done anyway.
A little background. I went to the heavy grease to try to take up some clearance on the P-10C, so that the barrel would lock up in exactly the same position from shot to shot. That gun's barrel has a little vertical play (0.008") and I could see it affecting the 100 and 200 yard groups. The heavy grease worked well in the C, so I tried it in the S and F, and left it in those guns although there was very little if any difference in groups at long distances, because those barrels are tight in the slide anyway. What I failed to anticipate is the gooey grease thickening up over time as the light ends evaporated. When it is first applied, it is fine. Apparently a month later the stuff thickens up. Not good for the tiny parts in a firearm, probably OK for heavy equipment.
Joe