Walt has the answer to keeping the new ones from cracking like the old ones. The garnish has a lip that keeps the flange part from seating flat against the ceiling, thus when tightening the screw, it bends/breaks the plastic flange. This is a design flaw present on almost every fan cover. Use the washers...
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired