Ok so an update...
So it is doing it again! Both a Symmetre and Sahara. Good news though...
I was always too lazy to open it up on a trip and usually ended up opening it at home. This never revealed anything as the reel works fine by then. I initially suspected viscosity change due to temperature as that was the only obvious variable that changed (being in the sun the whole day at the coast vs being stored and serviced under a roof). This time however I decided to start opening it up part by part cleaning, reassembling and function checking until I could find the root cause.... And viola it WAS the AR bearing this time round... A drop of water and the reel starts behaving erratically, almost like it partially engages in the forward direction if you stop or turn slowly. Dry it off with a cloth - done! Works like a charm. Could also explain why it seems to work better at home as the water may have had time to evaporate.
I still suspect that there is flat spot on the oscillating cam as explained earlier in this thread. Maybe a combination of both of these things.
