Kjell Olav
Slop-free is hard to find. One issue is that most top-performing servo's today has metal gears. Maybe a good idea for some use, for F3A it's not needed. My experience is first of all to avoid the metal gears. Before the JR DS8401 became available I used the 8411, but replaced the gears with plastic.
One additional reason for faster pot-wear today than with the old Sanwa's (and other non-digitals) is from the fact that the digital servos are much faster to correct errors on the output axle, and are much more precise. The combination of these to factors means that the sero tries constantly to correct for error-input generated by engine vibration. An example : a JR digital updates the output position at around 250 Hz (I have measured it, it's a little higher but I do not remember exactly), the fundamental frequency from the engine at 6000 RPM is 100 Hz. This means that the servo is constantly working to keep the aileron (or whatever) in corretc position by counter-acting the input from the engine vibration. With the old type of servo's the update frequncy is in the 50Hz range, and the servo does not 'understand' that the engine is shaking the surface up and down.
To sum up, there is a price to pay for the general improvement with digitals, even with slop-free gear-box the pot-wear is higher than in the old days.

Ola