I know one side is a 17mm but this side is much larger, anybody else who have had their swingarm off know what size it is?

If it's larger than 17mm and if it's 19mm a 3/4 6 point socket will work just fine. 18mm has to be 18mm to work.

All the hardware on the XT is sized metric. Conversions below:

17mm = .669"
18mm = .708"
19mm = .748"

So a 3/4" US socket is .002" larger than a 19mm bolt which won't matter. The other two smaller sizes are odd balls in US. Try a 3/4" (6 point only) socket and see if you get a proper fit. I'd also suggest getting a metric socket set if you plan on working on the bike. 6 point sockets will give better face contact and are recommended. A breaker bar is also a good tool to have for larger tougher to loosen bolts. If you get a metric socket set, find the socket that fits properly. Harbor Freight has THIS SET covering 10mm to 19mm in 6 point sockets. Not everyday rough service tools but good value for occasional usage. Good luck.

Thank you for the help guys, it was a 19mm, had to run to the shop to grab one. I've finally got it completely apart, and thankfully I did. There's practically no grease in them! One of the bushings are worn in the linkage but I already have a used one on hand. I'm cleaning it up now and am gonna pack it full of grease and call it a day

Mobil I full synthetic grease (red) is a good choice. Good luck effecting repairs.

Those bushings seem to be a weak point on the XT. Mine may be worn and I just don't know it. Everything feels tight, and it's not making any noise. I may order one of those linkages off eBay and rebuild it while the parts are still available.

I used to have a '79 Yamaha DT250, which had the original Monoshock, and it was so much simpler. No linkage. The swing arm was triangulated and the shock was mounted horizontally under the seat and tank. I don't remember ever having any issues with it, either mechanically or functionally. I guess Yamaha felt a need to make it more complicated.

Lube it via the 5 grease nipples, couple of squirts every 600 miles, then strip out & fresh grease every tyre change (3k miles) & it's all fine. Neglect & it's a rebuild. That grease Muniac recommends is what I use also.

Need a set of metric tools to work on Jap bikes + JIS screwdrivers or you'll chew up the crossheads.

I ended up using marine grease, its blue. Hopefully that works good, I read somewhere that it's really good for repelling water.
I got it all back together (forgot to take pictures because I was kinda stressed out) and now I notice a loud squeak from the top shock mount. (Cant be anywhere else i greased everything)
But I have no clue how to get in to thetop shock mount. Do I just take the seat off and its right there?

Honestly if theres no slop or noise I think you're fine. Mine had noticeable slop and would clunk a bit on bumpy roads and in general felt sloppy while riding. Now that I replaced the linkage, it's much better. It's not clunky anymore

That's the whole reason I did this actually. All the grease nipples were clogged and wouldnt accept grease(probably why they were dry) so I pulled them all off and soaked them in PBlaster to clean em