The Leica M4-P was the follow up to the M4-2. Production ran from 1981 to 1987 with the majority produced in Midland Canada. 

The M4-P continued the cost cutting production methods that the M4-2 started. The big change was a addition of frame lines for the 28mm and the 75mm lens. Total frame line are now a total of six and will become the standard for the M6, M7, and New MP. 

Cosmetically the major change is the addition of a Leitz red dot on the front of the camera. Not as obvious is that the top plate started as a brass with a stamped logo and over time shifted to a zinc cast top with the logo cast in to the top. There are also some reported variations with single synch outlets on the back (mine has the standard 2). Some of the late models had M6 top plates and the last 1,000 were supposedly assembled in Germany as the Canada plant was being phased out. Most of the M4-P were black chrome but they were also available in chrome.

The M4-P like the M4-2 have remained less attractive to collectors and perceived by some as less than the German Leica M bodies. Consequently, the price though still Leica, is less than most of the other M body options.

My Take:

Like the M4-2, the M4-P suffers from a perceptions problem. That did not translate to a performance problem in my experience. The fact that the Leica M is arguably over engineered as a basic light tight box means that there is lots of room before you get significant impact. The M4-2 and M4-P were still great cameras, even if not the peak Leica.

If you sleep with your Black M3 or MP, you may see a difference with the M4-P. But if you are new to Leica or not as set in your M use, the M4-P is a great camera. 

The M4-P is the last of the non-metered Leica (till the current MA) so you can read the light or use an external meter. I'm a fan of the Voitlander VC meter II.

The lens I use was a Soviet made Industar 61 (PT4765) 55mm f2.8. This is a mid 1980s lens that like the M4-P is under appreciated and thus lower priced. I payed $1.50 for this lens (postage to get it to me was $10). It is a screw mount lens so you need an adapter ring (I used one to map to a 50mm frame line). I understand that most people are not going to buy a Leica M (not even a M4-2 or M4-P) to use a $1.50 lens. Most will spend 100X or 1,000X that for a lens. Will they get 100X or 1,000X the results? Your call.

Lens: Industar 61 (PT4765) 55mm f2.8

Film: FujiColor 100

Links:

http://www.cameramanuals.org/leica_pdf/leica_m4-p.pdf

https://www.cameraquest.com/mguide.htm#M4-P

http://camerapedia.wikia.com/wiki/Leica_M4-P

https://en.wikipedia.org/wiki/Leica_M4

https://www.l-camera-forum.com/leica-news/2011/11/gear-reviews-leica-m4-p/

http://www.nemeng.com/leica/002bc.shtml