Hi mate,
I'm not familiar with the mechanics of this machine but the first things I'd do would be to check the springs are in good order, check that the drop target assembly is secure to the underside of the playfield, clean any coils and preferably change the sleeves. If the assembly looks like its has a lot of built up grime then it maybe best just to strip it down and clean it all properly. Depending on the assembly type they can be a pain though.
