help if you can please: I´ve tried 3 gaskets and 2 different covers(including the original) on my ´78 cb400t valve cover, it still leaks oil at the seal--only possible thing I can think of is that the relief tube on the top seems a little resistant when you take it off the valve cover and blow in it, otherwise I am stumped-cover/gasket appear to fir snug, but still leaks, no way it could have been bent, valve head is not warped..?!?!?