[Jim Hunter]

Hi,

You can clean them but be prepared for a messy job!
First of all you need a power washer.
Carb cleaner, oven cleaner and small wire brushes.

Apply oven cleaner let it sit for about an hour or so and wash off with water.
Carb cleaner is very HARMFUL use protective gloves and use only in WELL VENTILATED AREA with a little hard brush do the stubborn areas.
Wash again and see repeat one oven cleaner and one carb cleaner step until it comes clean.Magnesium is not as bright as aluminium so don't expect to get shinny.
You can paint it easily using some cans of Eastwood colors special made for magnesium.

Good luck