M4 van ICS met klein defect

I hereby put my M4, just over a year old, up for sale.
It has been through 3 days of play and still looks like new.
A few months ago new gears were installed, unfortunately a part was not placed properly, so it only shoots full auto, and not single shot. According to the store where I bought it, it was just a matter of opening it, placing the part correctly and ready, but they had so many repairs that they don't have time for me for the time being.
I'm not technical enough for this myself.
I am selling the replica without battery, I am also removing the tracer and the rifle scope visible in the photo.