Yep I'm a Hylomar blue man too! It's very sticky and won't set beyond a gel like finish and it really seals. As Richard V6 said though, re level the rocker box cover. They are always being over tightened and drag the area around the hole into a funnel shape. From my Ford days I have a tool I made to level them off. It's a cut down brick bolster with the sharpe edges just softened. I put the cover correct way up on a surface block, hard surface will do and slowly tap it back into shape. The bolster is 2 1/2" wide so flattens it perfectly. Use the cork gasket and Apply Hylomar blue, first to the rocker cover, here its fairly generous , 5mm centrally applied bead,then seat the cork gasket into it enough to just stick and position it. Now sparingly apply the Hylomar blue to the head surface..... Why not the cork I hear you ask! Well you don't want wodges of it squeezing out and finding its way into the oil with the obvious results. so a light smear here, start with a 3mm bead then smear it evenly on the surface. Now position the rocker cover onto the head.
Tighten down the cover, you may have to manipulate the cork gasket to align the holes with the rocker cover. Use a small screwdriver with gentle pressure applied downward on the cover and then fit the screw and engage the threads.... don't compress the gasket yet! When all screws are in, starting at the centre and much like tightening a head down, wrap the cover on evenly from side to side and diagonal to diagonal firstly just about finger tight then progressively tighter. You will not need more than a screwdriver type tool to achieve a tight enough fit! I Know Hylomar blue doesn't technically set but it does set up! If you can leave it over night before starting the engine then so much the better. That should sort your problem Dave.
If you find you still have a problem PM me and I have a few more suggestions for you to try!
