Exhaust joint leaks

This is normal they do not have a perfect seal, they have to be able to move do to vibration, expansion/contraction do to heat and cooling. Some thing has to give otherwise the exhaust port in the heads can be damaged or exhaust pipes crack/break. These exhaust joints need to be periodically maintained. with a high temp anti seize compound.

This exhaust system is indeed a pain. If you are doggedly persistent you can eventually eliminate the leaks or at least the big ones. It took me many, many iterations over several weeks of making minor adjustments by loosening all eight brass nuts at the cylinder heads (while leaving the joint springs in place) and shifting the muffler about, eyeballing the joints for a uniform fit, tighten everything up, fly it and recheck. Always apply a high heat anti seize paste and if you find a problem joint, bite the bullet and separate the joint, wipe clean the old paste from ball and socket ends, and reapply a liberal amount of new anti seize paste, and wipe away the excess after reassembly.  I used a copper based paste and it helps.