This is just me, but the most success in getting a Y-pipe to seal correctly is to make sure the sealing surface of the Y-pipe is perfectly flat. In the past I've seen too many Y-pipes warp and end up leaking in spite of using new gaskets during installation.
I realize this is a new pipe, but it's easy to check with a flat surface and a set of feeler gauges.
To answer your question, I would use an oem gasket, put the gasket in dry, and torque the bolts to spec.
Follow the oem torque sequence also.
Give me awhile and I will look up torque specs and sequence.

 

I like permatex gold between the cylinder and gasket.
Keep in mind ---I take stuff apart a lot :blink:, and this lets me reuse the gasket, as it stays stuck, to the cylinders.

 

I always use permatex gold also. I have the torque spec. From a 2013 rush manual that says 22 lb. I usually just snug them up pretty good. Can't usually get a torque wrench on all of them anyway. Always torque from the center out. I've heard of some guys using blue loctite, but I never have and never had a bolt back out yet.

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What is permatex gold? The spray on copper anti-seize?

 

I think they mean permatex ultra copper

 

Also a fan of ultra copper. Lil squirt / smear on bolt threads gives it additional resistance to backing off as well.