With my Glock 19 Gen 4, I have had to replace a few parts as well and it's been my main Carry Gun since the Gen 4 came out.

Now as we enter the wayback machine... I had one of the first ones in VA when it came into my shop as a "Blue Gun". I decided to act on Executive Privilege since I owned the shop I deserved one so I took it home.
Overall, it's been an excellent gun. It's been to a LOT of range trips, competitions, classes, etc. The finish on the slide is wearing around where it's been in a holster, and that's about it. Externally, these guns hold up well.

Incident 1:
Since I've owned it, I've had to replace the Recoil Spring Assembly 2-3 times. Time 1 was the "Recall that wasn't a Recall" This is where the 9MM 19 Gen 4s were supplied with the same RSA that the G-23 was. Guns had trouble cycling because they were oversprung. I never had issues, but took advantage of the deal. You had to call Glock and give your S/N. They offered 2 options, you could ship it in, or they'd ship the part. I had the part shipped. The other two times are just wear and tear. Like an oil change for a car. This is a known Glock "issue".

Incident 2:
This is where I learned the Single Point of Failure for the Glock system. At a pistol training course I commissioned for my shop and held at the Echo Valley Training Center in West VA, the slide shot forward of the locking block and almost came off the gun during recoil. Thinking this was a fluke, I pulled it back and it went into battery. I shot it again and the same thing happened. Once is a fluke, twice is "there's definitely something wrong here". I retired the Glock from the class and took up the S&W Shield instead. Diagnosis showed that the spring holding up the takedown latch had failed, badly. This simple 3 dollar part is a small thin piece of spring steel. Without it, the gun won't say in battery and the slide can possibly shoot forward of the barrel. Early Gen 4 19s had the Gen 3 part. This was rectified with a Gen 4 part. This is a known Glock "issue".

Incident 3:

I noticed some shots weren't going point of aim, but off to the right or left. Took me a while to figure out that the locking block was showing some wear on the left side. I pulled it out and replaced it with a new locking block. I returned to better shots and the new one doesn't show any signs of wear and tear as of yet. 

Modifications: 

I like to keep my guns for Carry relatively stock. I've changed out the Glock factory sights for Trijicon night sights. This is the first mod I do to any new to me Glock. 
Next, I changed out that idiotic serrated trigger with an OEM trigger from a Glock 17 gen 4. It's smooth and not serrated. After that, I popped in an OEM extended slide stop. It works better for me. After that was an NY-1 Trigger Spring. Again, OEM. And a "-" connector. Again, OEM. 
That's it. I've kept it stock otherwise using OEM parts where possible. Yeah, the trigger's a bit heavier, but with the "-" connector, the trigger is smoother. When there's no real "manual" safety like that on a 1911, I feel the increased trigger pull weight is necessary. 

That's my story and I am sticking to it.