1020 Seamaster second hand not working

Hi there,
I am new to this site. Recently I bought a 1020 Seamaster on EBay as spares or repair. It keeps good time, so I replaced the broken winding stem, double date wheel and dial feet screws. However the second hand only very occasionally moves despite the watch keeping time. I wondered if anyone could shed some light on this issue. Someone had obviously been in about the watch and done some damage/lost some parts prior to my acquiring it. Day star wheel is knackered, but expensive to replace.
Thanks in advance