Is it easy to fix faulty Skyray flashlights?

I purchased many Skyray flashlights from eBay recently.
I got the 3x, 4x, 5x, 6x, 7x, 8x and 9x.
For the most part, I love all of them but I think the best ones are the 4x, 8x and 9x.

Unfortunately two of them are defective. One is a Skyray 3x and the other one is a 6x.

The 3x initially could turn on and I could cycle through the modes.
However, after nearly 20-30 seconds, the flashlight can’t be turned off.
If I keep pressing the button every few seconds, it will go through high mode, low mode, high mode, high mode, low mode, high/low mode. So when it’s supposed to be off, it stays on.
The only way I could turn it on was by loosening the bottom half (battery compartment).
Now it has a new behavior. It is hard to turn on even with new set of unprotected 18650.
When it does turn on, it only turns on momentarily then turns back off in less than a second.
In fact, I don’t even have to press a button to turn on the flashlight, simply by gently shaking it the light may turn on momentarily.

The 6x initially turned on and behaved normally. Well, that lasted for a few minutes.
After playing with it for a few minutes, I found that it stopped working properly.
Now even with a fully charge set of unprotected 18650, the flashlight turn on very dimly on high mode, even dimmer on low mode. The output is so low that I can look directly at the emitters while on high mode without hurting my eyes.

My questions:

  1. What do you think cause these problems. It seems to me that there is a short-circuit inside the 3x. On the 6x, I suspect that the driver has a faulty/burned out transistor. I have not opened the flashlights because I am in the process of returning them to the seller.

2. Is it easy to replace bad electronic component(s)? I took electronics classes in college but that was many years ago. I can still solder but I need some help on what to do to fix the above issue.

3. If I have to replace the driver, I have heard about a few Skyray mods, where can I buy it and how much?

Thanks in advance!

Wow that’s a very fast reply! Thanks Ardvaark!
After a quick reading, I have more questions.
Since I am in no position to replace the stock MCPCB perhaps I only have one option, the 32x 7135.
Is it not an overkill for a SKR with only 3 XM-L emitters? I can imagine using it for the 6x.
Does it come with all the component soldered on or do I have to solder them myself?

Next, with more current, it will generate more heat and I learned that the SKR MCPCB is not secured / mounted to the flashlight body.
How do I improve heat dissipation?

Thanks again!

I have not opened the flashlights since I am negotiating with the seller whether to return them or to keep them with some compensation / partial refund. If we agree that I will keep the lights then I can open the inside.

It looks to me that all SKR 3x have problems. I have 3 of them and the other two are mostly functional but sometimes flicker.