Well I got sick of my fabbed valve covers leaking on my current headers and took them to the machine shop!!! They were pretty off along the rails and had serious sealing issues.... cost me $92 to have both milled flat and perfect... however they scratched them all up
I'll just paint them I guess... couldnt trash my new TTI Ceramic coated headers from stupid oil leaking and cooking on them!!!
I also noticed from tightening up the wing bolts that they had depressed into the aluminum making indentations or what ever and could have been some of the problem....
I recommend if you get a pair put them on and tighten them up then take them off and have them milled perfectly flat.... just tell them to be carfeul with them