I noticed one of the side-panels has started to crack from where it is bolted. I know these bolts are not tight, as I literally tightened them till I could not get a finger nail under the washer, and then 1-8th turn more. What material are these side panels? I have had to drill the leading edge of the crack to stop it running. Is there an option to buy metal side panels instead? A one-off request to have one cut is rather pricey. E3D should sell these in metal, or choose a less brittle plastic.