I returned from seven months in Afghanistan last April. My M3 was stored the entire time attached to a trickle charger and I followed all of the recommended storage techniques. I did take it to the dealership upon return for an oil change - zero issues and no problems. All components were solid and I am sold on the benefit of a trickle charger when not driving on a regular basis.
I think a trip to the dealership for an annual oil change and a good detailing will be what is needed.