Leaky rocker cover

My SP had a perfectly oil-tight engine until I decided to get rid of the original air cleaner arrangement and fit a Le Mans breather box and K&N filter. This means swapping the rocker covers left-to-right so the breather ports are on the front rather than the rear.
Ever since then I’ve had a leak from the right-hand rocker cover joint.
I’ve fitted a new gasket, then tried a thin smear of blue Hylomar but still leaking. Any tricks I should try? I’ve never had a problem on my loop, and I keep re-using the old gaskets on that when I do the valve clearances.

buy some new gaskets , you cheapskate

b4 fitting, stone off the surfaces

Oi cheeky - if you read the original post you’ll see I did get new gaskets for the SP, initially fitted with a smear of oil which normally works. When that failed I tried a tiny smear of blue Hylomar - still leaks. I can only think something isn’t flat? Might try 2 gaskets, although I did buy some different Loctite gasket stuff today.

Did you change the copper / alloy? washers on the breather pipes? Mine always weep a bit from there.

That makes sense as I have had rocker gaskets in 3 pieces which I refitted until my new ones came through, only to forget about them as they still refused to leak.
This was on big blocks. My lil’Breva will leak simply for the fun of it.

I’m pretty sure the leak is from the flange between the cover and head.

In that case take Baldrick’s advice and stone the surfaces.

Sheet of crocus paper, taped to a sheet of glass and dosed with light oil, then rub components in a figure of eight motion with minimal downforce, will do the job.

I thought I had a leaky rocker cover, spent ages trying to cure it. It turned out to be the Y shaped oil lines between the cylinders.