I remember seeing a quick link mentioned in a post about something called "Open Servo". It was an open source website about replacing the PCB inside an RC servo with a custom PCB so the servo could do more things over a serial connection instead of a PWM connection.
Does the person have the website for that? I can't find the post since I was just skimming and none of my searches come up with that website.
I don't think that this is what you are looking for but perhaps..... **broken link removed**
Are you talking about something like a small uC board that accepts serial and generates the standard servo pulses? I guess that if you remove the old board, then generating standard pulses wouldn't work.... Just what did it do?