I have only owned leverguns for a few years, but my .30-30 and .357 are both sensitive to ammo length.
When I press the OAL a bit shorter than book length, just 0.010" or less, action reliability increases a lot.
I still can get a hang, but holding/running the gun correctly in a big deal. It's easy to short-shuck.
On my 464 I spent lots of time polishing excess marinecote silver finish off the internal receiver.
If yours is Marinecote rather than blue, i'd look for spots where it seems to drag on the bolt.
The top of my hammer didn't ride solid on the bolt, but ran along one edge. The wear mark was evident.
I dressed the hammer off until it had good contact along the underside of the bolt.
I broke an extractor, when an overlength round stuck out of battery. They are weak so order a spare.
My hammer fall wasn't 100% solid. I had to bend the link which forces mainspring to hammer to remove the slop.
I did some other stuff I can't recall now, but it's all recorded in these pages if you look.