Over on the LXForums, the valve seat issue has happened to a couple of guys when they were driving the car, stopped for a short time (10-20 minutes) and when they went to start it back up, all hell broke loose with a valve seat falling out. Others it happened after the engine was seriously overheated.
Could if be that the valve seats don't have enough of an interfere fit, or poor maintenance? Maybe both. Something I thought it may be is from the infamous 5.7 HEMI "tick" from the pushrods being to short. Apparently the pushrods are to short and cause to much clearence in the valvetrain and make it noisy. In the opinion of others here, could this cause the valve to pound on the valve seat, causing it to work loose? I've never heard of a 6.1 HEMI dropping a valve seat and they don't have the "tick", as a matter of fact, the cure for the 5.7 is to use the 6.1 pushrods which are longer