seems I didn't join the transmission mount too well in the repair, not sure if maybe it isn't ABS even though it did seem to rub black on an acetone dampened paper towel. Anyway, here's the discovery and the new 3d printed part. maybe this will hold up better:

Cracked mount again, didn't notice until next day

3d parts at bottom, notice lack of gaps around screw threads, hopefully stronger

Fitting new part, collar not as pristine as before, but it's on.

mount looks a little cleaner than last job