Found a great way to fix Stern Flipper end of stroke buzzing.
Fashion a washer out of Automotive gasket material (I used gasket material 1.5mm thick)
Use the existing spring washer as a temp plate and pair of scissors to cut the outline and a drill to cut center.
I then moved the rear spring washer to the front of coil and used the fashioned washer to the rear.
WOW what a difference.