you really should spray them with a high UV Clear

Max 2K clear is the ticket as its a 2 part that self mixes in the spray can.
Did my lenses like 4yrs ago and still look like new

just sand them down with no finer than about 1000 to give the clear something to grip and spray

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2004 X5(E53) 3.0L
1999 M3(E36)
2003 Z4(E85) 3.0L