Eaton 18 speed play in gears

SO i spent a couple hours today taking things apart to pull my trans and do a clutch as well as possibly just throwing in a eaton reman trans from peterbilt.
I definitely need a clutch amungst other things while trans is out. Anyhow, after i removed my hydraulic pump and pto, i was able to look up in the trans and see a few things. In the video i took, you will see the gear set on the right appears to have up and down movement. I dont know exactly what im looking at. Im thinking maybe crosshsaft?? Any way, while im rotating the big gears, you will see the smaller gears on the right having what appears to be up and down movement, look at the dark shadow gap under that one gear.
Trans makes a rock crusher sound while creeping in low speed. Like gear sound. Anyhow, your thoughts on the video

 

no shrapnel on bottom plug just a little shaving material. The silvery mush material but not much. I had the auxillary done last year and the shop must be like all shops, they must reuse old oil from other peoples trans. The oil that came out of my trans was brown looking and nasty.
Soon as i get trans out tomorrow ill pop the top and take some pictures and a video of the gears to see if you see anything out of the ordinary.

 

howdy drivers, I got the trans out earlier. Couldnt find any carnage inside to show you so sorry about that. The input shaft and gear have alot of play and when you rotate, there is a alot of slop. Forgot to mention that 3rd and 7th arent that forgiving of gears to grab so i know there is an issue somewhere in that department as well. So that and the marbles in a can sound are the transmission issues i have. Here is video

 

i checked the diff magnets and only found a little bit of that sludge type metal specs that you normally find.
As far as the marbles in a can go, i verified the sound with people walking along side truck while creeping and definately coming from transmission. So its down to a wth going on. I could take the trans to a shop locally to have it gone through, but i think ill just call it a day and have peterbilt give me a reman and start fresh.
I have questions
My input shaft is a 10 spline, what tips can you give me to make life easier to reinstall the trans.
What bolts should i locktight.
Im installing a new flywheel as well.
Locktight with red or blue?
Locktight flywheel bolts and clutch bolts?
Any reason not to go with a 2 piece clutch brake?