I have a Bosch and the plastic snap-on cover rubs the clamshell. After 19 years it has rubbed the paint off, but I consider this normal as there is nothing I can do save for removing the plastic cover altogether.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)