As Jenne wrote, it does look like POP90 should be a god signal to use for an SRM dither lock, but somehow POP90 is not actually going to the ADS input matrix despite what the medm screens say, and what my old alog says.   I wonder if I frogot to check something into the svn after doing the model restart and someone reverted to the old version for some reason? 

Anyway, it seems worth getting the model with OPO90 in ADS back since a dither using POP90 might be an easy way to get SRM alignment under control now that the PD is no longer saturated.  Tonight it looked like the bounce mode rings up when SRM is misaligned, which makes sense if the SRM alignment causes SRC detuning and changes the DARM gain, as people have suggested.