Indeed many Arf tanks are problamatical and its not neccessarily related to how expensive the arf was either.

To avoid all the problems of a conventional expansion plug type consider a genuine Hayes 'O' ring type tank. Far more reliable and durable, can be assembled many times with no leakage and no adjustment as well as far easier to assemble. Perfect for two line systems and I use them for perhaps nine out of ten of my aircraft.

John