I have a set front and rear on the xm819, with slime, they slowly deinflate in about 24 hrs maybe loose 15 psi, but I think it's the slime. I'll be putting another tire in the rear, and seal both with Fix a Flat tubeless sealant (orange) which have worked ok with another wheelset (mavic x223) I have with maxxis rim strips and wtb mutano front, IRC trailbear rear. One thing I've noted is that the sidewall of the contis is more thinner than the other tires I have, and last week I hit a squared edge on a sidewalk a little hard and the tire got two holes and a bent rim edge. If it had a tube I'm sure it wouldn't have happened, it just gave up too easy and pressure was around 35 psi, another thing that may prove this is that when I first installed the tire, I inflated them with no Slime, just to test the sealing on the rim and almost instantly you could see little rubber bubbles on the sidewall, but with the Slime applied it didn't happen. Inflating them with no air compressor is a pain in the A$$. So always carry a tube. They are quite thin for a 2.3, looks more like an 2.2.
Good Luck!