Good stuff Bill.
Although the problems can't really be described as common to all Airfix kits, in this instance, the kit dates from the mid 1960's, with all that entails.
The company are in the process of slowly re-tooling most (probably all) of the more popular, older kits, some of which date back to 1952 !
They did go through a period, a few years back, where some then new kits, moulded 'overseas', although well detailed, suffered from horrendous fit problems with main components - the Buccaneer and Tornado F3, in 48th scale, being examples.