I'd first try cutting a piece from a steel allen bolt head to drop in where the missing piece is,pack it in tight with coke can shim against socket in stem ,with allen key already in place,(maybe araldite in allen socket/allen key interface) and try to gently undo bolt.Probably won't work but I'd try it
I'd first try cutting a piece from a steel allen bolt head to drop in where the missing piece is,pack it in tight with coke can shim against socket in stem ,with allen key already in place,(maybe araldite in allen socket/allen key interface) and try to gently undo bolt.Probably won't work but I'd try it