REMFLEX GASKETS BLOW OUT

I learned after installing the 4th, or 5th set of headers that leaked, that the head flange is anything but true.
Back in the day, I was installing 2 or 3 sets of headers, a coupla 3/4 race cams, and a few 4:11 gearset a week ! !
My mentor taught me how to "draw file", and insisted I did it on every header install.
Weld the valleys, file the high points till the mating surface is true.
I have seldom had a leak at the flange , use Mr Gasket or supplied gaskets, AND have never used a Remflex .