Sorry Dan, didn`t realise you were offering Rich the info....LOL...
I haven`t compared the servos side by side, but I do know that s12`s used the G32 or M32 servos whereas the s13 used the M195T servos. As Martin says the MC`s are totally different - the s12 has a bigger cylinder bore and different outlets.
I will compare the two servos next time I`m in the garage and post up the results
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Regards.
Ian.