firstly, your choice only you can decide.
secondly, how did mechanic know it was on the softest setting? did he set it himself? would anyone else there have known?? what would they have said???
were the tyres worn out or low or too high on pressure? that would make it wander, alternatively for a 32k mile bike could well have been wheel bearings or suspension bushes.
when was the fork oil checked or changed??
too many questions , dont blame yourself, if really interested you could get someone else to ride it as well.
