The Leyland DAF wings are notorious for corrosion. Due to poor design water and dirt sits between the support arms and the outer skin and this causes corrosion. Unfortunately due to the age of the trucks, most have this corrosion in the wings and it's almost unstoppable once it's started.
Motorcraft have taken a Mould from the original wings and offer replacement FRP wings that are almost identical to the original.
Leyland DAF wings (UK Nearside)
Note - This product is made to order. Allow 5-10 days for delivery.