Your P51 should not have hard start issues.
Did you get it restored/ adjusted by somebody??
Yeah that's what surprised me. It's inkes now with Namiki Blue and it has that issue. A little surprising since I'd figure the collector would ameliorate that. Once I'm done with the Namiki Blue I'll try Aurora Black and see if it just wants a wetter ink.
I haven't had it restored or adjusted... Got this off eBay about 13 years ago and in general it's a good writer.
Despite me kind of ripping into it, the P51 is a really good pen, and without the P51, it's doubtful there would be a Aurora 88, Lamy 2000 or Montblanc 12/14. (Though maybe someone else would come up with a great hooded nib.)
I think it was the first FP I had that was a good writer besides the Vanishing Point. I would have stuck with fountain pens back then but the feathering and bleed through in my hideous paper was pretty bad... And I didn't know about using other paper.
Still, after having other pens the past two years there are simply other pens I prefer more.