Use about a half of a can of Seafoam in the crankcase mixed with the oil----run about 100-150 miles, and then change the oil...Really did help my lifter noise(comes and goes)....
The Plate you are referring to is really a baffle to keep oil from spraying out of the PCV hole.Your grommet may be lodged there--Maybe use a shop vac???.
It may have just fallen onto the valve train somewhere--I would want to get it out....

1997 Wrangler TJ 5 speed, 2.5 L. Mostly stock except for 31x10.50's on Black Rockcrawler Rims.
1998 Wrangler TJ 5speed, 4.0L. Rusty's 3.5 " lift,33"BFG,4.10 gears,Novak transfer case shifter