doesn't john nikon f(*???) here do repairs?
*maybe wrong on the name
John,
I don't do repairs for other people. I'm not that skilled yet. I'd have no qualms doing an AI conversion ring swap on most Nikkors, but I don't trust myself to dig into an F3 and replace parts with the knowledge that it will work properly when I'm done.
That said, I did part out an F3P back in 2013. But, if I remember correctly, the F3P specific advance lever, shutter lock, and release assembly was sold back then. I only have a few pieces left from that body.
To the OP, I'd be tempted to just leave the camera as is. Since the mod was done by Nikon, it may become more valuable to someone. Plus, it does make the camera more useable in that you can use a cable release. Find another P for use when you want to have full weather sealing, or for putting on the shelf, if that was the original intention with the purchase of the $300 modified F3P off eBay.
-J