My muffler hanger has separated at the the rubber isolater donut thing, has anyone had luck gluing them back together and if so what did you used.

I drilled a hole thru the two pieces of metal and the “cushion” sandwiched… I used a 5/16” bolt with a nylon lock nut… Snugged… seems OK.
Sneezles61

When I’ve had that happen I took the metal bracket and rubber insulator in for sand blasting so surfaces are clean and rough. Then I used super glue on both pieces and clamped the parts together and let sit for a day. It’s held perfectly for several years. Oh yeah…I painted the part with high temp black paint like the rest of the exhaust. Looks completely stock.

You can buy new ones. I just did for my RT3.

Not sure what model the OP is talking about but the muffler stay for RT's are NLA from Yamaha.  Repops are available from KDI though.

Years ago mine had separated and I considered trying to fix it but I found a NOS piece on eBay pretty cheap.  Though It looked to me like a through bolt like Sneezle mentioned would be the best solution

It is for a 74 DT125, KDI only shows they make fork ca orings and a gas cap rebuild kit for that bike, not sure if one from another bike might ork though