Nick - the older SAS system is what the Mk3 Sea King has, a simplex system with limited authority requiring pitch and roll trim wheels to keep everything as central as possible. There is a control position transmitter for the cyclic to stop the system opposing pilot inputs.
On the 3A, the ASE computer is allowed acces to the pitch and roll beeper trims on the hyd pack, thus removing the need for trim wheels as it can always beep the cyclic back into authority.
There are FSLs in the control runs to stop the ASE fighting the pilot and the dead zone that these give has been dramatically reduced in the last few years by reducing the tolerances of the microswitches in them.
The problem is that just making the FSLs by moving the cyclic isn't always enough to change the attitude - I believe the 'attitude clamps' are a further element which has to be overcome by sufficient demand (cyclic movement) before the ASE computer gives up control (briefly).
The handling qualities change dramatically when the auto-trim element is bypassed by selecting manual trim - this removes the ASE computer from the equation and reverts to a more Mk 3 mode.