Ejection problem: Have you fired any other cartridges in your gun besides the Hornady Leverevolution? I have never had ejection problems with my several 336 Marlins. I'm not certain, but the Hornady ammo may be higher pressured than standard 30/30 ammo.
I have a Savage 30/30 and it will handle standard 30/30 ammo, but the cartridge will stick in the chamber with the slightest higher pressure loadings.
I have a 336 Cowboy in 30/30 and I just pulled it out of the safe to take shooting tomorrow.
I would try some standard Winchester or Remington loadings and if they don't eject way out, then you might consider calling Marlin. The Marlin people are great customer service specialists. The only Marlin that I have needed servicing is my 444 Marlin Texan. The throat eroded away and accuracy wained.
After 3,557 rounds it needed a new barrel. I sent it to Marlin. The gun had a 24" round barrel with a barrel strap instead of a cap. They replaced the fore end, the cap, the magazine tube and the barrel for $150. My original barrel was a micro grooved and it shot absolutely deadly accurate. The replaced it with a 22" bbl with Ballard rifling.
Harold Clark