Just a few thoughts on the exterior protection of the roof-mounted
hydraulic reservoir. Even though when a reservoir is sometimes
painted to match the aircraft colors, it is not a good practice for the
simple fact that, in addition to being a reservoir, it also acts as a
radiator to dissipate heat from the incoming fluid.
Paint adds that much more resistance to release heat. Just keeping
your magnesium reservoir protected with primer will suffice.
Hope this helps.