Minuscule Difference?
Perhaps you really should tryout these camera bodies before hand and not misinform others between the D810 & the D500/D5 before you think there is just a minor difference between them.
The D810 is a great studio and landscape camera with great low low ISO and better DR (Dynamic Range) over the D500 and the D5 combined.
Very different cameras for very different style of shooting.
For Starters, the D810 is a FF as the D500 is a DX 1.5x crop camera.
So knowledge will not make the difference when comparing these great fine instruments, they are just totally very different bodies overall and designed strongly for specific use.
Yes, I have used my D810 as a second body for sports for specific reasons, but prefer my D4s as I now use my D5 for the main camera for sports.
Hopefully my post will help you understand there is some major differences between the cameras.

Ive had many shutters and mirror boxes replaced from 3rd party companies and they have always reset the shutter count.
I wish Nikon would do the same.
Usually replacement of the shutter box requires to replace the shutter mechanism as well, so not unusual at all there.

i sent one well

True Story:
You obviously never owned a 1D MK III with its sub mirror reflex issues which created an auto focus sensor problem being overwhelmed in bright conditions.
This was a clear manufacturing error by Canon as they initially waited to fix the problem for some 4 weeks later, in the meantime I was stuck with (2) bodies that were rendered useless and resorted back to my trusted 1D MK2n because in the end I have to have happy clients.
I heard there were some out there that didn't have this issue because the blue dot was supposed to mean we were in the clear, but I had the blue dot models and they were still effected.
I also had to send in my 200 1.8, 300 2.8 IS, 400 2.8 IS to Canon so they could properly calibrate them with my MkIII bodies even after they supposedly fixed the sub mirror reflex issue.
This was during a spand of about 6months because I still needed to continue shooting for my clients during the peak season. In the meantime I bought a Nikon D3, thinking just to hold me down for a bit until I got the MKIII's fixed.
Guess what happened? I fell in love with the D3 and sold all my canon stuff, most of it here on FM many years ago.
Finally, The 1Dx is a great camera and certainly holds it own very well. The 7DII has seen a ton of use in the college and pro levels as several of my colleagues shoot with them.
So, yes Canon is back and doing great again.
But I certainly love my (2) Nikon D4s and D810 as well as my newest investment in the 400 FL lens.
I think many Canon shooters should thank Nikon for pushing Canon to get off of they're butts and produce some really nice precision instruments. We all benefit in the end..

I doubt it, but you never know.
I mean the 1st canon DLSR D30 came out in 2000 and was only a 3.5mp
and 15-yrs later were only @ 50mp with the D5s and I'm still not convinced its a true 50mp since the Nikon D810 (36mp) beats it in almost all major reviews Ive seen so far.
I personally think the large MP bit is very exaggerated and overrated.

Im not so sure about very little use, because my D810 had over 6K shots, but it was ok considering what I saved.

Yep, Im sure its nothing more than rumors.
BTW, Canon also makes fax machines too.
They will also soon make a 100 page per minute printers.
Or maybe it could just all be rumors..

Ive used 70% alcohol with Q-tips and an old tooth brush.
In some cases I've used the trusty wd-40 as it works to break
up the corrosion. Be surety only spray it on a rag or tooth brush and
not directly inside the compartment to avoid leakage into the electronic chips.

To OP:
You seem to spew out about Nikon this and that but nothing yet to back up your facts as Im still waiting to hear the complaints.
IMO, both Canon and Nikon have their issues.
Ive shot Nikon for 8 plus years now, but shot Canon for many more years from the Eos 3 & Eos 1V to the MKIII.
The main reason for the switch was the sorry excuse for a camera in the MKIII with it sub mirror reflex issues. BTW, the MKIV didn't fare to well either since the 7D appeared to be the weapon of choice for many pros until the 1Dx came out.
So, either bring forth some examples so we can properly comment about, or just put on your big boy panties yourself and save us the drama.

What exactly do you mean mixed reviews?
The 24-70 is a great lens and one of Nikon's best and sharpest lens for short to mid range. However, I will say that it is somewhat of a sensitive lens if bumped too hard.

Cheap DX lens with a top notch FF camera unfortunately will only waste your time as you will not be able to take advantage of a FF camera.
Best of luck.

One problem is too many people buy them to use over the weekend with the intention of returning them when done.
Ive seen so many of them abusing the system and returning several cameras.
There needs to be a 20% or more restocking fee to help prevent the abuse.
I frequent there several times a week for prints and I always here about the abuse from employees as well at the camera dept.
From what I hear, its mostly people from India who are doing this for long weekend weddings.

I'll eventually get one as it appears to be much better in overall all quality build. The original tends to be somewhat sensitive to normal pro abuse, causing it to get a little out of whack if bumped to hard.
Im looking forward to it.
Currently I have two in the shop via Nikon Service Center for not being as sharp to slightly blurred to the right side of the images.

Markins Q-20 or M-20 work great for me and also work better than competition for a monopod.
I personally have three of them dated back for the past 20 years.

Ive been using the back focusing (rocker effect) since 1999 back when I used canon gear.
I still shoot almost 90% of all my work, but Im mostly a sports shooter.
IMO, I have a much better keeper ratio with this method.
It takes some time to get used to it, so it may not be for all.
I personally recommend it for fast moving objects.
Hell, I just shot my niece's wedding this past Saturday for my own personal use and I still used the same method.