Okay, it's quarter after two in the morning and I found it.
I Googled
8FG delete entire memory and found an old thread where a guy was having the same problem with channels 3 and 7 linked. Turns out that the Function menu within the Linkage menu is where you assign functions to channels. Channel 7 had a VPP (I'm assuming variable pitch propeller) function linked to J3 - the throttle stick. When I removed the VPP function and went back to the servo menu, hey presto! Now channel 3 is no longer linked to channel 7!
Of course, now I have to prove to my satisfaction that the linking of throttle and ignition kill in the radio were responsible for burning out the throttle servos (which doesn't make sense to me)... or find another cause.
