Set your system vertical and try opening the tray. My bet is it won't open. It will try and get stuck. lord^infamous is right (I talked to him the other day)
This is a common problem among Xbox 1 Samsung drives as well. It is in fact a mechanical problem with the motor or motor belt. The motor that controls the tray opening/closing is the same motor that lowers the laser assembly. When this speed gets slower for some reason or because the rubber band stretches out, we run into two problems.
1. Tray getting stuck while ejecting. This motor lowers the laser assembly. When it cannot lower it fast enough, the tray is trying to eject while the assembly is still "up." The laser assembly is still stuck to the drive lid's magnet that holds the discs in place. That's why if your tray is getting stuck, if you get it a good whack on the lid of the drive, it opens. You "unstuck" the magnet, making the laser assembly move down, which then let your tray continue opening. If you don't believe me, take off your lid and you'll never get the tray getting stuck.
2. The other problem is what you stated, the drive refusing to stay closed. You try to close the drive and the motor doesn't close it hard enough. When this happens, the tray pops back out. I was having the same problem and can be seen on a video tutorial I made where I close the tray and it pops back out and I mutter "my stupid drive."
My drive was having both problems. My friend's drive is only having the first, where his drive gets stuck while opening. You seem to be only having problem 2. Thing is, they are related and when it gets worse, both problems will show up. Here is how I fixed both of my problems.

By using the rubber band instead of the belt motor, my drive has yet to get stuck once and has yet to close one time. Before this, I had a 0% eject rate while the console was vertical and at times I had to eject the tray in 9 times before it would stay closed. Now, I can open the tray every time, even in vertical. And I haven't had it refuse to close once. Just give it a try, might work for you. It did for me.