The servos probably have the old connector. I think they were called "F type". The newer Futabas have J type connectors. If the servos are still good, you could use them still, but you'd need to change the connectors. I did that recently on a few of mine, worked fine. I just cut the old connector off and soldered on a new wire. However, a simpler, and probably more reliable, approach is to just take them out and replace with new servos. You can get an entire 4 channel package for $80-100. Futaba S3004, or other standard size servos, should fit in the same holes as the S28 and S38 servos.