They should be waterproof. Heres the text of a post of mine yesterday in another thread.
The alloy luggage for the 12GSA is marketed as being waterproof by BMW, and says so in the small print. I've had 3 complete sets (panniers & top box) under warranty to get a set that were waterproof, and this 3rd set is perfect and have had them for nearly a year now. No issues with warranty claims for letting water in either, (once I showed the dealer where it said they were waterproof).
Heres the blurb that says they are waterproof:
"These robust, all-new panniers with plain aluminium surfaces have
a capacity of 44 litres on the right-hand side and 38 litres on the left.
Waterproof and securely lockable, they can carry up to 10 kilograms of
luggage, and feature stainless steel lashing eyelets, so that extra items
can easily be attached to the outside. The top box offers an additional
32 litres (5 kilograms) of carrying capacity."
Source:
Click here and then select P24 of the BMW accessory catalogue
Also, P32 for the "waterpoof" top box...
As there are various waterproofing ratings (IPx3, 4, 7 etc), IMHO, BMW are being rather naieve by claiming that a product is waterproof without specifying to what degree....