So basically you against buying used GPUs in general because you can't tell if it was mined or not.
Personally I don't mind buying used hardware except for hdd and ram because there is very little reason to sell those components by themselves unless something ain't right.
You know, after 12 pages of this back and forth it always seems like the ultimatum laid down is either "don't buy used" or "mining isn't so bad."
Why is this always the case?
Mining can suck for a card. Miners can run them near 100%, in a hot box, with little airflow. That's how we get to see the "reclaimed" new card with extreme yellowing. Your anecdote is that you ran a bunch of cards not inside of a hot box, and they're fine. That's great...but anecdotally my 470 is about 6 years old and still runs well despite being in a gaming rig because if you buy more than one fan you can keep the thing plenty cool enough not to have issues.
The problem with anecdotes is that they are not facts, but instances. We hear from the OP that they're absolutely bent on buying one of two cards, and will not consider an alternative. One is 3 generations behind, and the other is 2 generation and was confirmed to be mined on. The discussion has evolved to how to replace thermal pads...and the concept of Watts per meter per Kelvin is an ask to understand. We have officially gone from what do I buy, to justify my decision and tell me how to fix the thing. I'm unwilling to understand what some of this means, and me taking the cards apart is probably not a great idea, but I'm going to take apart a used card and recondition it...because I'm unwilling to buy anything else. It's like somebody hell bent on buying a used car with a decent sound system installed, instead of buying a cheap new one, because they're sure that they are getting a deal with the used car and can fix any issues despite not knowing a torque wrench from a box end wrench.
Sometimes it's a bad idea to be incapable of making a decision, because you're sure the one you've already committed to is the best one. Sometimes your lack of knowledge should stop you from doing something that you don't understand. Despite this, the OP seems to really want this...so people are trying to walk them through fixing up a card based off of a link to the GPU database and basic understandings of how things should perform.
This is a disaster waiting to happen, where one or more thermal pads isn't thick enough, doesn't conduct enough heat, or simply doesn't cover a high heat item and results in a card that quickly bakes itself into oblivion...making the OP's deal on a card basically go up in flames. I want to watch...but this is not a success story in the making. It's at best a moderate non-failure, and at worst a complete destruction of a card in the search to save some money doing something that you don't understand.
Let me share a real story with you. Two guys go out, and start a landscaping business. Three years later they call my dad, because their truck is having huge issues starting. Cracks open the hood, pulls the dipstick, and finds a black molasses. Asks "when was the last time you changed the oil?" and gets a perplexed look. "I was topping it off every few months." They genuinely thought that the oil inside of a work truck simply needed to be topped off...and this was two guys who had literally been working on farms their teen life, and they were about 26 at the time of the story. Sometimes instead of "knowing" you can do something you should just take the L, and either ask or pay for the thing to be right. This applies to automotive maintenance, and buying a video card. That said, the OP seems to want justification for their decisions rather than to discuss the merits of things...so I'm of the mind that morbidly watching the situation may lead to amusement...and I hate myself a little for it.
This isn't about whether you should buy a used card or not. This is about deciding to buy a used card, asking strangers their opinion, understanding that you should recondition the thing you're buying, and demonstrating that you probably shouldn't be doing this because it's beyond your knowledge to understand. That said, it's the OP's money and time. I'm just looking forward to the discussion in about a month that will follow, when they run a test and the performance is off...and the ask to solve the problem for them with nothing more than the low performance numbers...because that's (usually) how these things go.
Side note, thermal conductivity, or Watts/m*K represents how much energy is conducted. Watts is in joules/second, m is basically the pad thickness, and K is the delta in temperatures between surfaces. So...let's do some fun math.
k=6W/m*K
K = 90C-28C = 62K (since both are in C we adjust for component temperature and ambient)
m = 0.75 mm = 0.00075m
A = 1cm^2 (a square centimeter segment) = 0.0001m^2
Q=k*A*K/m = 6*0.00075*62/0.0001 = 2790 Watts
That seems really high, right? Well, no. The aluminum will heat up, meaning that you've got that K value decreasing over time, which is why GPU heat sinks get hot to the touch. Once that K value goes down to 5 degrees you'll see the energy transfer is 225 Watts of heat...which is much more in-line with wicking off enough heat to prevent baking.
Well, aluminum has a k value of 237W/m*K, or 39.5 times higher than that thermal pad. Why use a thermal pad then...as they seem to be less about transfer and more about thermal blanketing? Well, note that the area of contact is a big part of this equation. If A is trivial then you basically have a part without heat transfer...so a thousand fold increase in A is preferred even if it comes with a 40th the conductivity. That said, when you have hard measures you prefer to use ground surfaces and thermal paste...because metal on metal is better.
Also regarding the thermal pads, they're mostly an oil matrix with suspended solids doing the lifting work on real heat transfer. If you tighten them too much they generally crack and break, rapidly bringing that contact area down. You don't want to compress the pads a lot, only enough to make complete physical contact. Again, without real measurements this is a guess. Custom cards generally have their own measures. This is another difficulty in reconditioning a card...because the right option is to have the OP use a micrometer to measure these instead of guessing...
